CODE SCANNER

Car Computer Code Reader Domestic GM & Saturn ®

Lector de Códigos de Computadoras de Automóvil GM y Saturn nacionales de EE.UU. con Systemas MCU y EEC-IV (para EUA) Instrucciónes en español - página 99

Tensión: 14V Para Nombre, Domicilio y Telefono Hecho en: China del Importador: Ver Empaque 1 2 ®

Congratulations on purchasing your Code Scanner for accessing engine trouble codes required for repairing vehicles equipped with computers. You can have confidence this product maintains the highest quality in manufacturing, and will provide you 1 About Codes ...... 5 years of reliable service. 2 When to Read Codes ...... 7 3 Reading Codes ...... 8 4 Using Codes in a Basic Troubleshooting Procedure ...... 12 5 Code Meanings ...... 16 This instruction manual is divided into 6 Additional Code Scanner several key sections. You will find Diagnostic Features ...... 24 detailed steps on using the Code 7 Computer Basics ...... 27 Scanner and important information about trouble code meanings, how a 8 Glossary ...... 33 computer controls engine operation, and more! Identifying the problem is the first step in solving that problem. Your 9 ABS Basics ...... 40 Code Scanner can help you 10 ABS Safety ...... 46 determine by accessing the engine 11 ABS Tips ...... 47 computer trouble codes. Armed with that knowledge, you can either refer 12 Reading ABS Codes ...... 49 to an appropriate service manual or System 1: Bosch 2S ...... 53 discuss your problem with a knowl- System 2: Bosch 2U (Version A) ...... 58 edgeable service technician. In either event you can save yourself a lot of System 3: Bosch 2U (Version B) ...... 64 valuable time and money in auto System 4: Bosch 2U (Version C) ..... 70 repair. And feel confident that your System 5: Teves Mark II (Version A) 76 vehicle’s problem has been fixed! System 6: Teves Mark II (Version B) 81 System 7: Kelsey-Hayes RWAL ...... 86 System 8: Kelsey-Hayes 4WAL ...... 90

Applications ...... 96

3 General Safety Guidelines to follow when working on vehicles • Always wear approved eye protection. • Always operate the vehicle in a well ventilated area. Do not inhale exhaust gases – they are very poisonous! • Always keep yourself, tools and test equipment away from all moving or hot engine parts. • Always make sure the vehicle is in park (Automatic transmis- sion) or neutral (manual transmission) and that the parking brake is firmly set. Block the drive wheels. • Never leave vehicle unattended while running tests. • Never lay tools on vehicle battery. You may short the terminals together causing harm to yourself, the tools or the battery. • Never smoke or have open flames near vehicle. Vapors from gasoline and charging battery are highly flam- mable and explosive. • Always keep a fire extinguisher suitable for gasoline/electrical/ chemical fires handy. • Always turn ignition key OFF when connecting or disconnect- ing electrical components, unless otherwise instructed. • Always follow vehicle manufacturer’s warnings, cautions and service procedures.

CAUTION: Some vehicles are equipped with safety air bags. You must follow vehicle service manual cautions when working around the air bag components or wiring. If the cautions are not followed, the air bag may open up unexpectedly, resulting in personal injury. Note that the air bag can still open up several minutes after the ignition key is off (or even if the vehicle battery is disconnected) because of a special energy reserve module.

4 available from the manufacturer, other publishers or your local public library. The computer system in today’s vehicles does more than control engine operation – it can help you find problems, too! Special testing abilities are permanently programmed into the computer by factory engineers. These You obtain trouble codes from the tests check the components connected engine computer memory by using the to the computer which are used for Code Scanner tool. Refer to section 2 (typically): fuel delivery, idle speed for details. After you get the trouble control, spark timing and emission codes, you can either: systems. Mechanics have used these • Have your vehicle professionally tests for years. Now you can do the serviced. Trouble codes indicate same thing by using the Code Scanner problems found by the computer. tool! or, • Repair the vehicle yourself using trouble codes to help pinpoint the problem. The engine computer runs the special tests. The type of testing varies with manufacturer, engine, model year etc. There is no “universal” test that is the same for all vehicles. The tests examine To find the problem cause yourself, you INPUTS (electrical signals going IN to need perform special test procedures the computer) and OUTPUTS called “diagnostics”. These procedures (electrical signals coming OUT of the are in the vehicle service manual. computer.) Input signals which have There are many possible causes for “wrong” values or output circuits which any problem. For example, suppose don’t behave correctly are noted by the you turned on a wall switch in your test program and the results are stored home and the ceiling light did not turn in the computer’s memory. These tests on. Is it a bad bulb or light socket? Is are important. The computer can not the bulb installed correctly? Are there control the engine properly if it has bad problems with the wiring or wall switch? inputs or outputs! Maybe there is no power coming into the house! As you can see, there are many possible causes. The diagnostics written for servicing a particular trouble code take into account all the possibili- The test results are stored by using ties. If you follow these procedures, you code numbers, usually called “trouble should be able to find the problem codes” or “diagnostic codes.” For causing the code and fix it if you want example, a code 22 might mean to “do-it-yourself.” “throttle position sensor signal voltage is too low.” Code meanings are listed in Section 4. Specific code definitions The Code Scanner makes it easy vary with manufacturer, engine and to fix computer vehicles model year, so you may want to refer to a vehicle service manual for additional Using the Code Scanner to obtain information. These manuals are trouble codes is fast and easy. 5 Trouble codes give you valuable trouble codes are and where they come knowledge – whether you go for from, you are well on your way to fixing professional vehicle servicing or “do-it- today’s computer controlled vehicles! yourself. ” Now that you know what

6 • The “Check Engine” light comes ON when the engine is RUNNING or, Light ON and stays ON (when the • Vehicle engine is running poorly and engine is RUNNING) “Check Engine” light is OFF. – The computer sees a problem that does not go away. (A “hard” failure.) – The light will stay on as long as the problem is present. The engine computer turns the “Check Engine” light on and off as needed. – A trouble code is stored in computer memory. (A “hard” code.) – Use the Code Scanner at the earliest convenient time to obtain codes. Refer to section 3, “Reading Codes”.

Light ON and then goes OFF (when the engine is RUNNING) This dashboard message light is either – The computer saw a problem, but amber or red and labeled: the problem went away. (An – “Check Engine” or, “intermittent” failure.) – “Service Engine Soon” or, – A trouble code is stored in computer – “Service Engine Now” or, memory. (An “intermittent” code.) – marked with a small engine picture. – The light went out because the problem went away, but the code stays in memory. – Use the Code Scanner at the earliest convenient time to obtain The “Check Engine” light is normally codes. Refer to Section 3, “Reading OFF when the engine is RUNNING. Codes”. NOTE: The computer will automati- NOTE: The light will come on when cally erase codes after several restarts ignition key is in ON position, but the (typically 50) if the problem does not engine is OFF. (For example, before return. you start the engine.) This is a normal test of all the dashboard message lights.

If the “Check Engine” light does not come on, you have an electrical Most likely this condition is not due to problem which needs repair. Refer to computer system failures - but reading the “Diagnostic Circuit Check” steps in codes can still be useful as part of a the “Basic Diagnostic Procedures” basic troubleshooting procedure. section of your vehicle service manual. Review Section 4, “Using Codes” before proceeding to Section 3, “Reading Codes”. 7 1) Safety First! • Set the parking brake. • Put shift lever in PARK (automatic transmission) or NEUTRAL (manual transmission). • Block the drive wheels. • Make sure ignition key is in OFF position. • The connecter is located under the dashboard on the driver’s side. 2) Test the “Check Engine” Light Exceptions: (Also called “Service Engine Soon”, –LeMans: Located behind passen- “Service Engine Now” or labeled ger side kick panel. Remove snap- with a small engine picture.) on cover for access. • Turn ignition key from OFF to ON –Fiero: Located in the center position, but do not start the console behind cover panel. engine. –Corvette: Sometimes located in • Verify that the light turns on. centerconsole behind ashtray. Consult service manual for exact ON location. • The connector may be in full view, or

F

F it may be recessed behind a panel. O An opening in the panel allows access to recessed connectors. • If the light does not turn on, you have a problem with this circuit which must be repaired before proceeding. Refer to the “Diagnos- tic Circuit Check” procedure in your vehicle service manual. • Turn ignition key OFF.

• The connector may have a slip-on cover labeled “Diagnostic 3) Have a Pencil Connector.” Remove cover for and Paper testing. Replace cover after Ready testing. Some vehicles require this This is for cover in place for proper operation. writing down all the codes. 5) Verify Ignition Key is OFF

4) Find the Computer Test Connector FF ON • Service manuals call this connec- O tor the Assembly Line Diagnostic Link (ALDL) connector. It may also be called the Assembly Line Communication Link (ALCL) or simply test connector. 8 6) Plug the Code Scanner into the sequence is repeated. This continues Test Connector. Put TEST switch until the ignition key is turned OFF (so on ENGINE. you can double check your code list).

Example of code 12 only:

Car Computer Code Reader ❊ PAUSE ❊❊

TM FLASH (pause) FLASH FLASH (longer pause) ❊ PAUSE ❊❊ • The Code Scanner only fits ONE FLASH (pause) FLASH FLASH WAY into the test connector. (longer pause) • The Code Scanner will not harm the vehicle engine computer. ❊ PAUSE ❊❊ NOTE: The Code Scanner does not FLASH (pause) FLASH FLASH use all of the test connector contacts. Also, one Code Scanner (even longer pause, then start over again) pin may plug into an empty test connector position. This is normal. Example of code series 12 and 24:

7) Turn Ignition Key to ON Position ❊ PAUSE ❊❊ but DO NOT START THE ENGINE FLASH (pause) FLASH FLASH You may hear some clicking sounds coming (longer pause) from under the hood. This is normal. WARNING: Stay away from the ❊ PAUSE ❊❊ radiator cooling fan! It may turn on. FLASH (pause) FLASH FLASH (longer pause) 8) Get Codes from the Flashing “Check Engine” Light ❊ PAUSE ❊❊ NOTE: If the light does not flash, you have a problem which must be FLASH (pause) FLASH FLASH repaired before proceeding. Refer to even longer pause, then go to next code) “Diagnostic Circuit Check” chart in vehicle service manual. Count flashes to get trouble codes. ❊❊ PAUSE ❊❊❊❊ Code 12 looks like: FLASH FLASH (pause) ❊ PAUSE ❊❊ FLASH FLASH FLASH FLASH (longer pause) FLASH (pause) FLASH FLASH (FLASH = 1, FLASH FLASH = 2. ❊❊ PAUSE ❊❊❊❊ Put 1 and 2 together = code 12.) FLASH FLASH (pause) FLASH FLASH FLASH FLASH Code 23 looks like: (longer pause) ❊❊ PAUSE ❊❊❊ PAUSE FLASH FLASH (pause) ❊❊ ❊❊❊❊ FLASH FLASH FLASH FLASH FLASH (pause) • Each code is flashed three (3) times FLASH FLASH FLASH FLASH before the next trouble code is sent. (even longer pause, then start all over • After all codes are sent, the whole from the very beginning) 9 • A code 12 is always sent even 9) Turn Ignition Key OFF when the computer sees no problem. This tells you the computer diagnostic checks are 10)Remove Code Scanner and Re- working properly. If you do not get install Connector Cover, if a code 12, or if the “Check Engine” supplied. light does not flash you have a The computer system is now back problem which must be repaired. to normal operation. Refer to “Diagnostic Circuit Check” procedure in vehicle service manual. 11)Refer to “Test Results” chart on page 11. • All codes are two (2) digits long. • Codes are sent in numeric order from the lowest number to the This completes the code reading highest. procedure. At this point you can either: • Have your vehicle professionally The engine computer can send trouble serviced. Trouble codes indicate codes for transmission problems - if problems found by the computer. the vehicle has a computer controlled or, transmission. • Repair the vehicle yourself using NOTE: Some diesel powered trucks trouble codes to help pinpoint the have a computer controlled transmis- problem. sion. These vehicles will only send transmission related codes since the the diesel itself is not computer controlled. • GM Vehicles –The “Check Engine” light flashes both engine codes and transmis- sion codes. • Saturn Vehicles –The “Check Engine” light flashes engine codes. –The “Shift to D2” light flashes transmission codes. Look for a code 11 flashed on the “Check Engine” light. This is a signal telling you transmission codes will then be flashed on the “Shift to D2” light. Transmission codes are flashed in a way similar to engine codes.

10 TEST RESULTSCOMMENTS

No indication on • You have a problem which needs repair “Check Engine” before using the Code Scanner. light • Refer to “Diagnostic Circuit Check” chart or, in vehicle service manual. Did not receive Code 12.

Code 12 only. • Computer did NOT find a problem. • If a driveability problem persists, perform “Visual Inspection” and “Basic Mechanical Checks” (Section 4, “Using Codes”.) • Refer to “Diagnosis by Symptom” charts in vehicle service manual. (Additional electrical and mechanical checks are listed.)

Received Code 12 • Computer found problems in vehicle. along with other • Follow steps in Section 4, “Using Codes”. codes. • Code definitions are in Section 5, “Code Meanings”. – GM engine and transmission codes start on page 16. – Saturn engine codes start on page 16. • Saturn vehicles only: Code 11 means transmission codes are flashed on “Shift to D2” light. – Saturn transmission codes start on page 21.

11 Using Codes Using Trouble Codes as Part of a Basic Troubleshooting Procedure

HVAC A driveability problem can have many Information YST CRUISE CE BOOSTER

EGR possible causes which are not related VAC (VECI) BRAKE BOOSTER G GAP REG

FUEL PRESS to the computer system. Reading REG. decal TO TRANS MODE U.S.A. EGR VAC codes is one part of a good trouble- located in REG shooting procedure consisting of: FRONT the engine EM OF CAR 1) Visual Inspection compart- ment. 2) Basic Mechanical Checks –Pinches and kinks. 3) Reading Codes –Splits, cuts or breaks. 4) Using the Vehicle Service Manual • Inspect wiring for: 5) Erasing Codes –Contact with sharp 1) Visual Inspection edges. Doing a thorough visual and “hands- (This on” underhood inspection before happens starting any diagnostic procedure is often.) essential! –Contact You can find the cause of many with hot drivability problems by just looking, surfaces, such as exhaust thereby saving yourself a lot of time. manifolds. • Are routine maintenance items –Pinched, burned or chafed O.K.? insulation. – Clean air filter –Proper routing and connections. – Correct fluid levels • Check electrical – Recommended tire pressure connectors – Good ignition system components for: - spark plugs, wires and the like. –Corrosion • Has the vehicle been serviced on pins. recently? –Bent or – Sometimes things get recon- damaged pins. nected in the wrong place, or not –Contacts not properly seated in at all. housing. • Don’t take shortcuts. –Bad wire crimps to terminals. – Inspect hoses and wiring which Problems with connectors are may be difficult to see because of common in the engine control system. location beneath air cleaner Inspect carefully. Note that some housings, alternators and similar connectors use a special grease on components. the contacts to prevent corrosion. Do • Inspect all vacuum hoses for: not wipe off! Obtain extra grease, if –Correct routing. (Hoses may be needed, from your vehicle dealer. It is missing or misconnected.) Refer a special type for this purpose. to vehicle service manual, or Vehicle Emission Control

12 • “Hard” codes – codes for problems Don’t overlook the basic checks listed which are present now. on the next page. Mechanical problems • “Intermittent” codes – codes for by themselves can always create engine problems which happened in the troubles. Even worse, these problems past, but are not happening now. can make a good sensor send an Remember... incorrect signal to the computer. Then the computer runs the engine improp- –“Check Engine” light ON: You have erly or sets a trouble code. at least one “hard” code stored in memory. (You may have more • Cylinder compression: “hard” or “intermittent” codes

–Check for proper 150 180 stored, also.) 120 210 9 90 12 compression in 6 15 240

60 – “Check Engine” light OFF: Stored 3 18 30 COMPRESSION each cylinder. TESTER 21 270 codes are for “intermittent” –Refer to vehicle 300 problems. (Exception: sometimes service manual for there are minor “hard” faults which specifications. do not turn on the “Check Engine” • Exhaust backpressure: light.) –Check for any restrictions in the How to Tell “Hard” Codes from exhaust system. “Intermittent” Codes • Ignition timing (If adjustable): Do the following if you are not sure: –Verify timing is within • Write down all codes (except code specification. 12). For example: 15, 34.

Made in U.S.A.

CP7515 INDUCTIVE TIMING LIGHT • Erase codes from computer –Refer to memory. (Refer to Step 5.) vehicle • Drive vehicle for at least 10 minutes service manual, at normal temperature, cruise speed or Vehicle and load. (The computer may want Emission Control to verify a fault for several minutes Information before storing a code.) (VECI) decal located in the • Read codes again. Codes which engine compartment. return are “hard” faults. Codes which do not return are “intermittent” faults. –Be sure to disable computer spark For example, if you see code 15 (but advance timing circuit, if used, not 34) then you know code 15 is a when checking basic timing! “hard” code and code 34 was • Air induction system: “intermittent”. –Check for You troubleshoot the “hard” problems intake differently from the “intermittent” ones. manifold vacuum leaks. –Check for Dealing with “Hard” Codes carbon or • Refer to varnish the vehicle build-up on throttle valve or idle service speed control device. manual diagnostic code charts. Refer to Section 3, “Reading Codes”. Remember there are two types of codes: 13 • Follow all the steps in the diagnostic Dealing with No Trouble Codes procedure for the trouble code. Have a driveability problem, but only get • Be sure to erase the trouble codes code 12? Make sure you do Step 1, from computer memory after “Visual Inspection” and Step 2, “Basic completing repair work. (See Step 5, Mechanical Checks”. If you did not find “Erasing Codes from Computer the problem, then refer to “Diagnosis Memory”.) by Symptom” charts in vehicle service • Drive vehicle for at least 10 minutes manual. at normal temperature, cruise speed and load. – Read codes again to verify trouble code is gone (problem fixed). Other Erase codes from memory whenever codes may have been repaired at you complete a repair or to see if a the same time! problem will occur again. Note: The computer will automatically erase codes after several restarts (typically Dealing with “Intermittent” Codes 50) if the problem does not return. These codes are for problems which happened in the past, but are not present now. • Usually these problems are due to Proceed as follows: loose connections or bad wiring. • Observe all safety precautions. (See The problem cause can often be page 4.) found with a thorough visual and “hands-on” inspection. (Refer to • Turn ignition key ON. Step 1, “Visual Inspection”.) • Insert Code • Refer to the vehicle service manual Scanner. Car C om put Make sure er Code R

diagnostic code section. You can not TM ea der use the code chart procedures TEST switch because they are for “hard” is in ENGINE problems - those which are present position! T E S T now. However, the charts have • Turn ignition key ABS ENGINE suggestions for dealing with OFF. intermittents and can tell you where • Remove the bad connections, etc., might exist. ECM fuse You can also refer to the “Diagnosis from the by Symptom” charts. fuse block • Be sure to erase the trouble codes for 10 from computer memory after seconds. completing repair work. (See Step 5, • Replace “Erasing Codes from Computer fuse. Memory”.) • Remove • Drive vehicle for at least 10 minutes Code Scanner. at normal temperature, cruise speed and load. If ECM fuse cannot be located, then – – Read codes again to verify trouble • Disconnect power to the computer. code is gone (problem fixed). To do this: Other codes may have been –Disconnect repaired at the same time! the positive battery terminal “pigtail”, OR

14 –Open the in-line fuse holder going to the positive battery terminal, OR Use the GM method, or proceed as –Disconnect negative battery follows: terminal – but this will also erase • Observe all safety precautions. (See other items too, such as digital page 4.) clock settings and preset digital radio tuning. Warning: Stay away from the engine cooling fan. It may turn on • All the trouble codes are now during this procedure. erased from computer memory! • Wait thirty (30) seconds. 30 • Turn ignition key ON, but DO NOT SECONDS START THE • Reconnect power ENGINE. to the computer. T E S T • Put TEST switch ABS ENGINE The IMPORTANT: on ENGINE. computer has a “learning” ability to take care of minor variations in engine • Plug and control operation. Whenever you erase unplug the Code the computer memory by disconnect- Scanner ing power, the computer has to into the test “relearn” various things. Vehicle Car Comp

uter connector Co performance may be noticeably de R ead TM different until it “relearns.” This 3 times er temporary situation is normal. The within 5 “learning” process takes place during seconds. warm engine driving. • All the trouble codes are now erased from computer memory! • Turn ignition key OFF. • Remove Code Scanner and re-install connector cover, if supplied.

NOTE: • The engine control computer is usually called ECM (Engine Control Module) or PCM (Powertrain Control Module) in the vehicle service manuals. • Information flags and “Intermittent” codes may not by erased using this procedure. The presence of these codes will not cause any driveability or future self-diagnostics problems.

15 send an incorrect • Code meanings can 1) Visual inspections are signal to the computer vary with vehicle, important! and generate more trouble codes! model year, engine 2) Problems with wiring type and options. and connectors are • If a code number has common, especially This page: (Codes from more than one for intermittent faults. flashing “Check Engine” definition listed, note 3) Mechanical problems light.) that that only one (vacuum leaks, • GM engine codes definition applies to binding or sticking • GM electronic your vehicle. Consult linkages, etc.) can transmission codes service manual to get make a good sensor the specific definition send an incorrect • Saturn engine codes and troubleshooting signal to the computer. Page 21 (Codes from procedure for your This can cause a flashing “Shift to D2” vehicle. Trouble Code. light.) • Follow vehicle service 4) Incorrect information • Saturn electronic manual procedures to from a sensor may transmission codes find the cause of the cause the computer to code. control the engine in Refer to Section 4, the wrong way. Faulty “Using Codes” for engine operation troubleshooting tips and could even make a steps to erase codes different good sensor from computer memory.

(Saturn transmission code list begins on page 21)

Transaxle codes present Coolant temperature RPM signal problem. (Saturn). sensor (CTS) - signal OR voltage is low. Whenever code 11 is sent, Camshaft sensor - circuit it means transmission problems. codes will be flashed next OR on the “Shift to D2” light. Coolant temperature Refer to page 19 for Saturn sensor (CTS) - signal Electronic Control Module transmission code list. voltage is high. (ECM) computer circuit problem - Pull-up resistor (Saturn). Diagnostic test is working Battery or alternator problem properly. (Engine computer - voltage too high or low. verifies no RPM Reference OR Camshaft or Crankshaft sensor - circuit problems. Pulses are present during Direct ignition system engine off testing.) (DIS) fault - line open or OR shorted to ground. Fuel Injector circuit is not OR working properly - possible Oxygen (O2) sensor - blown fuel injector fuse. signal stays low (“lean”) Ignition system fault - Loss during warm engine cruise of 2X or Low Resolution Pulse signal. or sensor circuit is open or Ignition system fault - left sensor circuit is open OR Intermittent 7X signal or (dual sensor models). Transmission speed error. loss of 58X signal or 6X signal (Saturn). 16 21 29 34 Throttle position sensor 4th gear switch. Mass air flow (MAF) sensor (TPS) - signal voltage is OR - signal voltage or high during engine idle or frequency is low during deceleration. Quad-Driver module or engine cruise. Quad-driver No. 3 error. OR 22 OR Manifold absolute pressure Throttle position sensor Secondary air injection (MAP) sensor - signal (TPS) - signal voltage is system - circuit problems. voltage is low during low during engine idle. 31 ignition on. OR Manifold absolute pressure OR Fuel cutoff relay circuit - Pressure sensor circuit - open or shorted to ground. (MAP) sensor - signal voltage is low. signal voltage too high or 23 OR low (carburetor engines). Manifold air temperature Fuel injector. 35 (MAT) sensor - signal OR Idle air control (IAC) voltage is low or high. Park/Neutral switch - system problem - can not OR circuit problems. set desired RPM. Throttle position sensor OR 36 (TPS) error. CAM sensor - circuit OR problems. Mass air flow (MAF) sensor - burn-off circuit problem. Mixture Control (M/C) OR OR solenoid - open or short Engine speed control circuit problems. governor malfunction. Transmission shift problem (Van) (electronically controlled 24 transmissions only). OR Vehicle speed sensor OR (VSS) - open or short Turbocharger wastegate overboost. Direct ignition system (DIS) circuit problems. fault - loss of 24X signal or OR extra or missing pulses in 25 Wastegate electrical signal electronic spark timing Manifold air temperature - open or shorted to (EST) signal. (MAT) sensor - signal ground. OR voltage is low. OR Ignition system fault - loss OR Purge solenoid voltage of High Resolution Pulse Vacuum switching valve high (carburetor engines) signal. circuit - open or shorted to ground. 32 37 OR Barometric pressure (BARO) Brake switch stuck “on”. ATS sensor - signal sensor circuit failure. voltage is high. OR 38 26 Exhaust gas recirculation Brake switch circuit fault. (EGR) valve diagnostic OR Quad-Driver module or switch - closed during Knock sensor (KS) - open Quad-driver No. 1 error. engine start-up or open circuit problem. when EGR flow requested 27 by ECM. 39 2nd gear switch. OR Torque converter clutch OR EGR/EVRV. (TCC) circuit fault. Quad-Driver module or 33 OR Quad-driver No. 2 error. Clutch switch circuit 28 Mass air flow (MAF) problems. sensor - signal voltage or OR 3rd gear switch. frequency is high during engine idle. Knock sensor (KS) - short OR circuit problem. Quad-Driver module or OR Quad-driver No. 3 error Manifold absolute pressure (Corvette). (MAP) sensor - signal OR voltage is high during engine idle. (Note: Engine (Transmission) Fluid mis-fire or unstable idle pressure switch assembly may cause this code.) - open or short circuit problems.

17 41 Power steering pressure Voltage reference error. Cam sensor (CAM) failure. switch failure. OR OR 47 Vehicle anti-theft system (VATS) problems. Cylinder select error. Electronic control module OR (ECM) computer circuit 54 problems - universal Tach input error - no Low fuel pump voltage. reference pulses during asynchronous receiver/ engine run. transmitter (UART) link or OR data loss. OR Fuel pump relay. OR Electronic spark timing OR (EST) circuit - open or Knock sensor module EGR Solenoid No. 2 shorted to ground during located in the computer is failure. engine run. not working properly. OR OR 48 Quad-Driver module (QDM) output failure. Direct ignition system Misfire symptom. (DIS) fault - bypass circuit OR OR open or shorted to ground Mixture Control (M/C) during engine run. Mass air flow (MAF) solenoid - circuit voltage OR sensor - open or short too high. circuit MAF sensor signal. Ignition system fault - loss of 1X Reference Pulse 49 55 signal. Electronic control module High idle RPM or vacuum (ECM) computer circuit 42 leak (Saturn). problems - ECM failure, Electronic spark timing 51 serial bus error, SAD error (EST) circuit - open or or fuel lean malfunction. Electronic control module shorted to ground during OR engine run. (ECM) computer circuit problems - faulty EGR Solenoid No. 3 OR programmable read-only failure. Direct ignition system memory (PROM), MEM- (DIS) fault - bypass circuit CAL, ECM or checksum 56 open or shorted to ground errors. Corrosivity/add coolant. during engine run. 52 OR OR Port throttle system Fuel cutoff relay circuit - Electronic control module vacuum sensor problems. open or shorted to ground. (ECM) computer circuit problems - faulty or missing OR 43 CALPAC or MEM-CAL, Quad-Driver “B” fault. analog to digital converter Electronic spark timing (A/D) error or Quad-Driver 57 (EST) circuit - low voltage module (QDM) fault. detected. Boost Control problem. OR OR 58 Oil temperature sensor - Electronic spark control signal voltage is low Vehicle anti-theft system (ESC) - circuit problems. (Corvette). (VATS) problem. 44 OR OR Lean exhaust indication - System voltage high for a Transmission Temperature long period of time. Sensor (TTS) - short circuit oxygen (O2) sensor voltage stays low after one or two (Electronic transmission problem in sensor or minutes of engine run. note: this fault may cause wiring. (Left sensor on dual other codes to be set.) OR sensor engines.) Transmission fluid 53 temperature high. 45 Over voltage condition. Rich exhaust indication - (Electronic transmission 59 note: this fault may cause oxygen (O2) sensor voltage Transmission Temperature stays high after one minute other codes to be set.) Sensor (TTS) - open circuit of engine run. (Left sensor OR problem in sensor, on dual sensor engines.) Exhaust gas recirculation connector or wiring. 46 (EGR) - system problems OR or EGR Solenoid No.1 Transmission fluid Vehicle anti-theft system problem. temperature low. (VATS) failure. OR OR

18 61 66 Vehicle Speed Sensor (VSS) - loss of signal. Oxygen (O2) sensor Air Conditioner (A/C) degraded. pressure sensor - circuit 73 OR problems or low A/C charge. OR Air Conditioner (A/C) Port throttle system error. evaporator temperature OR Electronic Control Module sensor - signal voltage too (ECM) computer circuit high. Cruise control problems - problem - internal reset vent solenoid circuit. occurred. OR OR OR (Transmission) Pressure Air Conditioner (A/C) control solenoid - circuit (Transmission) 3-2 shift problems. system performance control solenoid - circuit problems. problems. 74 62 67 Traction control circuit voltage low. Gear switch circuit Cruise control - switch problems. circuit problems. 75 OR OR Exhaust gas recirculation Oil temperature sensor - Air Conditioner (A/C) (EGR) system - Solenoid signal voltage is high pressure sensor - circuit No.1 problem. (Corvette). problems. OR OR OR System voltage low - Cruise control problems - Torque Converter Clutch charging system problems. vacuum solenoid circuit. (TCC) solenoid - circuit OR 63 problems. Transmission voltage low - Manifold absolute pressure OR low system voltage (MAP) sensor - signal Cruise control switches - possibly caused by voltage is high. circuit problems. generator voltage supply circuit or power train OR 68 control module (PCM). Small EGR failure. Cruise control - system OR circuit problems. 76 Exhaust gas recirculation Right oxygen (O2) sensor OR failure (dual sensor (EGR) system - Solenoid Air Conditioner (A/C) No.2 problem. engines). clutch relay - short circuit. OR OR 77 Cruise control system (Transmission) Overdrive Exhaust gas recirculation problem. ratio error - engine RPM (EGR) system - Solenoid 64 greater than input speed. No.3 problem. Manifold absolute pressure 69 OR Primary cooling fan relay (MAP) sensor - signal Air Conditioner (A/C) voltage is low. driver circuit - circuit system - pressure switch problems. OR or A/C clutch relay circuit Medium EGR failure. problems. 78 OR OR Secondary cooling fan Torque converter clutch relay driver circuit - circuit Right oxygen(O2) sensor - lean condition indicated stuck “on”. problems. (dual sensor engines). 70 79 65 Air Conditioner (A/C) Vehicle Speed Sensor Large EGR failure. pressure sensor - signal (VSS) - signal voltage too OR voltage too high. high. Fuel injector current low. 71 OR OR Transmission Temperature Air Conditioner (A/C) Sensor (TTS) - high Right oxygen (O ) sensor - evaporator temperature 2 temperature indicated. rich condition indicated sensor - signal voltage too (dual sensor engines). low. 80 OR 72 Vehicle Speed Sensor Cruise control position (VSS) - signal voltage too sensor problem. Gear Select switch - circuit low. problems. OR 19 Brake switch circuit Electronic control module Electronic control module problems. (ECM) computer circuit (ECM) computer circuit OR problems - faulty problem - internal reset programmable read-only occurred. Anti-Lock Brake System memory (PROM). (ABS) message fault (Saturn). OR Skip shift light - open or OR (Transmission) Input or output speed sensor - short circuit problems in (Transmission) Solenoid circuit problems. (Speed skip shift light circuit. “B” (3-2 shift solenoid) - sensor signals do not open or short circuit agree with with selected problems. gear range.) Pressure control solenoid - OR transmission line pressure not at desired level. Ignition system fault - 3X Torque converter clutch signal problem. (TCC) - TCC is mechanically stuck on. OR Change oil light - wrong Electronic control module voltage is present in light (ECM) computer circuit circuit for more than 26 Electronic control module seconds. problem - internal (ECM) computer circuit communications failure problems - faulty analog- (Saturn). to-digital (A/D) converter. OR Transmission voltage low - OR low system voltage (Transmission) Solenoid (Transmission) Low gear possibly caused by “A” (1-2 shift solenoid) - error - transmission in 3rd generator voltage supply open or short circuit or 4th gear when computer circuit or power train problems. commanding 1st or 2nd control module (PCM). gear. OR Torque Converter Clutch Low oil light - wrong voltage is present in light (TCC) solenoid - circuit Electronic control module problems. circuit for more than 26 (ECM) computer circuit seconds. OR problems - faulty Reverse Inhibit - open or electrically erasable programmable read-only short circuit in reverse Vehicle speed sensor inhibit solenoid coil. memory (EEPROM). (VSS) - output circuit OR problems. (Transmission) High gear 3-2 Control solenoid - open error - transmission in 1st or short circuit problems. or 2nd gear when Tachometer output circuit OR computer commanding 3rd problems. Skip shift solenoid - open or 4th gear. or short circuit problems.

20 (GM/Saturn engine codes and GM transmission code list begins on page 16.) Note: Code numbers labeled “Information Torque converter clutch Flag” may be sent along stuck”on”. Powertrain Control Module with the regular (PCM) computer circuit (unlabeled) trouble problem - communication codes. The computer interrupt failure. Quick quad-driver output sends Information Flags fault - open or short circuit to help you find the on any of the qaud-driver Hold mode voltage is too cause of a trouble code. module circuits (QDM) that low. Note that conditions lasts 5 seconds or longer. OR which only cause an Information Flag will not Transaxle temperature Reference input turn on the “Check circuit open. intermittent or noisy - Engine” light. Refer to missing or extra ignition vehicle service manual reference pulses are detected by powertrain Transaxle temperature troubleshooting charts. control module (PCM). circuit grounded.

Gear selector error signal. Powertrain Control Module Line pressure high. (PCM) computer circuit problem - communications failure. Powertrain Control Module Line pressure low. (PCM) computer circuit No turbine speed signal. problem - serial link data invalid.

Turbine speed signal Hot light. noise. Hold mode stuck “on”. OR

No 1st gear. Vehicle Speed Sensor OR (VSS) circuit - no signal. Battery voltage out of range - battery voltage has dropped below 11 volts or Electrical variable orifice has increased above 17 (EVO) fault. Vehicle Speed Sensor volts. (VSS) circuit - signal noise.

Hold mode stuck “off”. No gears available. OR Master relay - open or grounded. ESC (Knock present) - 2nd gear stuck “on”. powertrain control module (PCM) can not reduce engine knock by retarding No 2nd gear. Master relay - shorted. timing.

No 3rd gear. Powertrain Control Module Gear selector switch circuit (PCM) computer circuit problem - no signal. problem - analog to digital No 4th gear. (A/D) converter error. OR

No torque converter clutch. Gear selector switch circuit 5-volt reference ground - problem - invalid signal. flag will set if manifold

21 absolute pressure (MAP) 63 71 sensor signal, handwheel (Information Flag) (Information Flag) sensor signal, throttle position sensor (TPS) Powertrain Control Module 2nd line circuit - grounded signal are zero volts. (PCM) computer circuit or open. problem - Random Access OR 55 Memory (RAM) failure. (Information Flag) OR Transaxle temperature Cooling system high sensor failure. (Information Flag) temperature - engine 56 Option check sum error - coolant temperature is flag will be set if tire size greater than 239°F (Information Flag) and options do not (118°C). Generic Field-Effect compare with those stored Transistor (FET) driver in the powertrain control 72 failure. module (PCM). (Information Flag) 57 64 2nd line circuit - shorted. (Information Flag) (Information Flag) OR (Information Flag) Powertrain Control Module Powertrain Control Module (PCM) computer circuit (PCM) computer circuit Cooling system low problem - non volatile problem - Electrically temperature - engine Random Access Memory Erasable Programmable coolant temperature is less (RAM) failure. Read-Only Memory (EE than 32°F (0°C). PROM) failure. 58 73 (Information Flag) 65 (Information Flag) (Information Flag) Battery voltage unstable - 3rd line circuit - grounded battery voltage changes Ignition voltage problem - or open. more than 3 volts too high or low. OR instantaneously. 66 (Information Flag) 61 (Information Flag) Coolant sensor signal (Information Flag) unstable - coolant Clamp shorted. temperature sensor (CTS) Powertrain Control Module indicates a change of more (PCM) computer circuit 67 than 59°F (15°C) problem - Programmable (Information Flag) instantaneously. Read-Only Memory Clamp open. (PROM) failure. 74 OR OR (Information Flag) (Information Flag) (Information Flag) 3rd line circuit - shorted. Handwheel sensor circuit 6X Signal fault - 6X pulses fault - handwheel sensor OR do not occur between output voltage is out of (Information Flag) each reference pulse or a tolerance. 6X pulse does not Coolant/Transmission immediately follow a 68 temperature sensor ratio reference pulse. Possible error - indicates a degrading open or intermittent in DIS (Information Flag) coolant temperature sensor module harness. Line circuit grounded or (CTS) if transmission open. temperature sensor (TTS) is 62 working properly. 69 (Information Flag) 75 (Information Flag) Powertrain Control Module (Information Flag) (PCM) computer circuit Line circuit shorted. problem - interrupt failure. 3rd gear stuck “on”. OR (Information Flag) Air temperature sensor signal unstable - air temperature sensor (ATS) indicates a change of more than 59°F (15°C) instantaneously.

22 76 83 92 (Information Flag) (Information Flag) (Information Flag) 4th line circuit - grounded Transaxle temperature Clamp circuit - intermittent or open. low. fault. OR OR 93 (Information Flag) (Information Flag) (Information Flag) Throttle position sensor Low coolant - coolant (TPS) to manifold absolute switch opens for 20 Torque Converter Clutch pressure (MAP) sensor seconds with engine (TCC) hold circuit - voltage out of range - flag running. intermittent fault. is set if TPS and MAP 94 voltage readings dont 84 agree with internal (Information Flag) (Information Flag) relational tables stored in Brake switch stuck open. Master enable relay circuit the powertrain control - intermittent fault. module (PCM). 85 95 (Information Flag) (Information Flag) 77 Brake switch stuck closed. (Information Flag) Line circuit - intermittent 86 fault. 4th line circuit - shorted. (Information Flag) 96 Engine speed invalid. 78 (Information Flag) (Information Flag) 87 Torque Converter Clutch (Information Flag) (TCC) circuit - intermittent 4th gear stuck “on”. fault. Torque Converter Clutch (TCC) hold circuit - 97 79 grounded or open. (Information Flag) (Information Flag) 88 2nd gear circuit - Torque Converter Clutch (Information Flag) intermittent fault. (TCC) circuit - grounded or open. Torque Converter Clutch 98 (TCC) hold circuit - (Information Flag) shorted. 81 3rd gear circuit - intermittent fault. (Information Flag) 89 (Information Flag) Torque Converter Clutch 99 (TCC) circuit - shorted. Master relay stuck “on”. (Information Flag) 91 4th gear circuit - 82 (Information Flag) intermittent fault. (Information Flag) Assembly Line Diagnostic Transaxle temperature Link (ALDL) - serial unstable. communication link interrupt.

23 This section contains... “driver”). The computer energizes the Relay and Solenoid Circuit Test: You coil by using the transistor switch. can switch on most of the computer Transistor ON: controlled relay and solenoid circuits - – Transistor electrically connects end for checking relay operation or making of coil to circuit ground. wiring voltage checks. – Coil is ON because circuit is Field Service Test (Fuel Injected complete. (Coil connected to battery Engines Only): A quick check of the power and ground.) fuel control system to verify proper operation. Transistor OFF: Become familiar with Code Scanner – Transistor disconnects end of coil use (Section 3) before using the from circuit ground. following procedures. – Coil is OFF because circuit is open. (Coil not connected to circuit ground.) You can switch on most of the computer controlled relay and solenoid circuits except the fuel pump relay and Computer controlled relay and solenoid fuel injectors. This is helpful for coils are commonly wired as follows: checking relay operation or making • One side of the coil is connected to wiring voltage checks. Do the following: a source of vehicle battery power. • The other side of the coil is wired to 1) Safety First! the computer. • Set the parking brake. Inside the computer housing is a • Put shift lever in PARK (automatic transistor switch (often called a transmission) or NEUTRAL (manual transmission). RELAY COIL • Block the drive wheels. • Make sure ignition key is in OFF position. COMPUTER 12 volts or more 2) Plug the Code Scanner Less than 1.5 volts into the Test Connector. Transistor ON* Put TEST switch on ENGINE.

*Transistor action is

shown using a “switch” Car Com

put er RELAY COIL representation for Cod e Re ad TM clarity. er

T E S T COMPUTER ABS ENGINE 12 volts or more 12 volts or more Transistor OFF*

24 3) Turn Ignition Key to ON Position but DO NOT START THE ENGINE. • WARNING: Stay away from the radiator cooling fan! It may turn on. This is a quick check of the fuel control • Ignore the flashing Check Engine system to verify proper operation - light. especially after repair work. Service manuals call this the “Field Service Mode”. Do the following: 4) Computer Controlled Relays and Solenoids are Turned ON Exception: Fuel pump and fuel 1) Safety First! injectors are OFF. (Refer to vehicle • Set the parking brake. service manual for any other • Put shift lever in PARK (automatic exceptions.) transmission) or NEUTRAL • Make any relay or (manual transmission). solenoid circuit V RPM • Block the drive wheels. 10 Megohm OFF X10 750 4 CYL 5 CYL checks at this 200 6 V 20 CYL 8 2 CYL • Make sure ignition key is in OFF 4 20 time. Note the CYL M 5 2M CYL 200 6 position. K CYL following special 8 Dwell 20K CYL circuit actions... Ohms 2K 200 – Fuel Injected 2) Test the “Check Engine” Light Engines Only: (Also called The Idle Air “Service Engine Control (IAC) Soon”, “Service motor fully extends (most vehicles) Engine Now” or or moves back and forth. labeled with a small engine picture.) – Carbureted Engines Only: The • Turn ignition key from OFF to ON Idle Speed Control (ISC) motor, if position, but do not start the used on vehicle, moves back and engine. forth. Also, the Exhaust Gas Recirculation (EGR) solenoid is • Verify that the light turns on. energized for 25 seconds. • If the light does not turn on, you have a problem with this circuit which must be repaired before 5) Turn Ignition Key OFF. proceeding. Refer to the “Diagnos- • Remove Code Scanner and re- tic Circuit Check” procedure in your install connector cover, if supplied. vehicle service manual. • The computer system is now back to normal. 3) Start the Engine • This completes the Relay and Solenoid Circuit Test. WARNING: Always operate vehicle in well ventilated area. Exhaust gases are very poisonous!

4) Plug the Code

Car Com

Scanner into put er Cod e Rea

TM the Test der Connector. Put TEST switch on T E S T ENGINE. ABS ENGINE The engine computer is now in the “Field 25 Diagnostic Mode.” The flashing • Light mostly ON while flashing: “Check Engine” light shows how the system is running “rich”. fuel control system is operating. • Light mostly OFF while flashing: See below. system is running “lean”. Read Section 7, “Computer Basics” Various mechanical, electronic or or Section 8, “Glossary” for an wiring problems can cause the explanation of Open Loop and computer to sense a “rich” or “lean” Closed Loop operation. running engine. Usually these IMPORTANT: The oxygen sensor conditions will generate a trouble code, needs to be hot so the computer such as 44 (lean exhaust) or 45 (rich can check the signal for proper fuel exhaust). Follow vehicle service delivery. Warm the engine by idling manual troubleshooting charts to find for 2 minutes at 2000 RPM. Then, the cause. The Field Service Test lets gently rev the engine from idle to you check to see if the problem was part throttle several times. (This fixed. (Light flashing equally ON and creates a changing sensor signal OFF once a second.) for the computer.) Finally, keep the Note: While in the “Field Service throttle steady, or at idle, for the rest Mode”... of the test. – New trouble codes are not stored in computer memory. – On some engines, the computer will send a signal for a fixed spark advance. The computer is in Open Loop 5) Turn Ignition Key OFF operation. The computer will run • Remove “open loop” if it does Code Scanner Car Compute not see an oxygen sensor signal r Code Re

T a M because... and re- der install – The oxygen sensor is not hot connector enough to operate (normal cover, if condition if engine too cold or supplied. sensor cooled down during idle) • The or, computer – Open circuit problems exist (bad system is sensor or wiring). Note that this now back condition will generate a trouble to normal. code. • This completes the Field Service Test.

The computer is in Closed Loop operation. The oxygen sensor is sending a signal. • Light equally ON and OFF while flashing: system is running correctly (proper air/fuel mixture). 26 COMPUTER BASICS What does the Engine Control Computer do?

This section further explains the engine What has NOT changed? computer control system, the types of A computer controlled engine is sensors and how the computer controls basically the same as earlier types. It is fuel delivery, idle speed and timing. still an internal combustion engine with The following is an introduction to pistons, spark plugs, valves and cams. computer controlled engine systems. The ignition, charging, starting, and Additional information may be found in exhaust systems are almost the same, books dealing with this subject as well. You test and repair these available at your local library or auto systems the same way as before, parts store. The more you know about using familiar tools. The instruction the computer system, the better and manuals for these tools show you how faster you can troubleshoot and fix to perform the tests. Your compression problems. gauge, vacuum pump, dwell-tach meter, engine analyzer, timing light, Why Computers? etc., are still valuable! Computer controls were installed in vehicles to meet Federal Government The Engine Computer Control regulations for lower emissions and System better fuel economy. This all began in The computer module is the “heart” of the early 1980’s when purely mechani- the system. It is sealed in a metal box cal control systems just were not good and linked to the rest of the system by enough anymore. A computer could be a wiring harness. The computer programmed to precisely control the module is located in the passenger engine under various operating compartment, usually behind the conditions and eliminate some dashboard or front kick panels. This mechanical parts making the engine protects the electronics from moisture, more reliable. extreme temperatures and excess Note that vehicle service manuals refer vibration, which are common in the to the computer as either the ECM engine compartment. (Engine Control Module) or PCM The computer is permanently (Powertrain Control Module). programmed by factory engineers. The program is a complex list of instruc- What the computer controls tions telling the computer how to control the engine under various The main control areas of the computer driving conditions. To do its job, the are: computer needs to know what is • Fuel delivery happening and then it needs devices to control things. • Idle speed • Spark advance timing Sensors give the computer • Emission devices (EGR valve, information carbon cannister, etc.) The changes made to the basic engine The computer can only work with to allow a computer to control these electrical signals The job of the sensor tasks are the only differences between is to take something the computer an older engine and a computerized needs to know, such as engine one. A little later we will discuss just temperature, and convert it to an how the computer handles these tasks. electrical signal which the computer

27 (voltage signal to the computer) or INPUT SENSORS OFF (no voltage signal to the computer). Switches connect to two wires and tell the computer simple things, such as whether or not the air conditioner is running.

OUTPUT BRAINS OF THE ACTUATORS • Signal Generator – These create COMPUTER their own signal to tell the computer of some condition, such as exhaust can understand. gas oxygen content, camshaft You can think of sensors as “high tech” position, or intake manifold vacuum. senders the devices found in older They may have one, two or three vehicles for gauges and dashboard wires connected to them. message lights (oil pressure, fuel level, etc.) Signals running into the computer are referred to as “inputs.” The computer controls things with Sensors monitor such things as: actuators • Engine temperature The computer can only send out • Intake manifold vacuum electrical signals (referred to as “outputs”). Devices called actuators • Throttle position are powered by the computer to • RPM control things. Actuator types include: • Incoming air (temperature, amount) • Solenoids – These are used to • Exhaust gas oxygen content control a vacuum signal, bleed air, control fuel flow, etc. Most engine computer systems will use the sensor types listed above. • Relays – These switch high Additional sensors may be used amperage power devices on and off, depending upon the engine, vehicle such as electric fuel pumps or type or other tasks the computer must electric cooling fans. do. Note that information from one • Motors – Small motors are often sensor may be used by the computer used to control idle speed. for many different tasks. For example, engine temperature is something the Other output signals computer needs to know when controlling fuel delivery, spark timing, Not all of the computer outgoing idle speed and emission systems. The signals go to actuators. Sometimes sensor information may be very information is sent to electronic important for one engine control modules, such as ignition or trip function, but only used to “fine tune” a computer. second one. How the computer controls fuel There are several types of sensors delivery • Thermistor – This is a resistor Good performance and low emissions whose resistance changes with depend upon precise fuel control. temperature. It is used to measure Early computer controlled vehicles temperatures of coolant or incoming used electronically adjustable air. It has two wires connected to it. carburetors, but fuel injectors were • Potentiometer – This signals a soon introduced. position, such as throttle position or The job of the computer is to provide EGR valve position. It connects to the optimum mixture of air and fuel three wires: one for power, one for (air/fuel ratio) to the engine for best ground and one to carry the position performance under all operating signal back to the computer. conditions. • Switches – These are either ON 28 The computer needs to know: expecting a certain amount of fuel to be • ...what the engine operating delivered. (The computer assumes condition is. everything in the fuel system is operating as expected.) In open loop Sensors used: coolant temperature, operation, the computer has no way of throttle position, manifold absolute checking the actual amount of fuel pressure, mass air flow, RPM. delivered. Thus, a faulty fuel injector or • ...how much air is coming into the incorrect fuel pressure can change the engine. amount of fuel delivered and the Sensors used: mass air flow or a computer would not know it. combination of manifold absolute The computer system is forced to pressure, manifold air temperature, operate “open loop” because no RPM. sensor type is available which can • ...how much fuel is being delivered. measure air/fuel ratios when the engine is cold. The computer knows this by how long it turns on the fuel injectors. (The computer uses a “feedback Hot engine cruise condition control” or “duty cycle” solenoid on An example of “Closed Loop” electronic controlled carburetors.) operation... • ...that everything is working the way The computer watches the coolant it should. temperature and throttle position Sensor used: exhaust gas oxygen sensors to tell when the engine is all sensor. warmed up and cruising. As before, Note: Not all engines use every sensor the computer determines the amount listed above. of air coming into the engine, then delivers the amount of fuel that should provide the optimum air/fuel mixture. Cold engine warm-up condition The big difference is that this time the An example of “Open Loop” opera- computer uses the oxygen sensor to tion... check how well its doing and re-adjust things, if needed, to make sure the fuel The coolant temperature sensor tells delivery is correct. For example: If the the computer how warm the engine is. oxygen sensor indicates a “rich” Factory engineers know what the best condition, the computer will compen- air/fuel mixture is for the engine at sate by reducing fuel delivery until the various operating temperatures. (More oxygen sensor signals an optimum air/ fuel is needed for a cold engine.) This fuel ratio. Likewise, the computer will information is permanently pro- compensate for a “lean” condition by grammed into the computer. After the adding fuel until the oxygen sensor computer knows the engine tempera- once again signals an optimum air/fuel ture, it determines the amount of air mixture. coming in, then it will look at its programming to find out how much fuel This is an example of “Closed Loop” to deliver and operate the fuel injectors operation. The control system accordingly. (Engines with electronic performs an action (expecting a carburetors don’t do any of this. They certain result), then checks the results have a thermostatically controlled and corrects its actions (if necessary) choke just like non-computer engines.) until the desired results are achieved. This process is an example of “Open The oxygen sensor only works when it Loop” operation by the computer. The is very hot. During cold engine warm- control system performs an action up, and sometimes at idle, the sensor (expecting a certain result), but has no will be too cool to operate (no signal way of verifying if the desired results sent). The computer must operate were achieved. In this case, the "open loop" during this time because it computer operates a fuel injector cannot use the sensor to check the air/ fuel ratio. 29 Acceleration, deceleration How the computer controls and idle conditions spark advance timing As long as the engine and oxygen You set spark timing in a non-computer sensor are hot, the computer can engine by using a timing light and operate “closed loop” for best economy adjusting the distributor at idle RPM. and least emissions. During the drive During vehicle operation, timing is conditions listed on the left, the changed by either engine vacuum computer may have to ignore the sensor (vacuum advance function) or by engine and run “open loop,” relying on internal RPM (centrifugal advance function.) programming for fuel delivery instruc- These spark timing changes are done tions. During idle, for example, the mechanically inside the distributor. oxygen sensor may cool down and stop Computer controlled vehicles using a sending a signal. A different situation distributor still have you set spark timing can occur during wide-open-throttle by using a timing light and adjusting the acceleration. The computer sometimes distributor at idle RPM. The timing adds additional fuel (on purpose) for changes which occur during vehicle temporary acceleration power. The operation, however, are controlled computer knows it is running “rich” so it electronically. The computer looks at ignores the sensor signal until the wide- sensors to determine vehicle speed, open-throttle condition is over. engine load and temperature. (RPM, throttle position, coolant temperature How the computer controls idle and manifold pressure or mass air flow speed sensors are used.) Then, the computer adjusts timing according to factory Throttle position and RPM sensors tell programmed instructions. Some the computer when the vehicle is vehicles have a “knock” sensor. The idling. (Sometimes an idle position computer can “fine tune” the spark switch on the throttle is used.) The timing if this sensor signals an engine computer simply watches RPM and knock condition. A timing signal (“EST” - adjusts an idle speed control device Electronic Spark Timing) is sent by the on the vehicle to maintain the desired computer to an ignition module which idle condition. Note that this is another eventually creates the spark. The example of “closed loop” operation. computer uses a crankshaft position The computer performs an action sensor to determine piston position, so (activating an idle control device), it can send the spark timing (EST) then watches the results of its action signal at the proper moment. (engine RPM) and readjusts as Newer ignition systems use no necessary until the desired idle speed distributor. There are several versions, is achieved. such as Computer Controlled Coil There are two types of idle speed Ignition (C3I), Direct Ignition System control devices. The first is an (DIS), Integrated Direct Ignition (IDI) adjustable throttle stop that is and Opti-Spark. These systems use positioned by a computer controlled multiple ignition coils. (2 spark plugs motor. The second method lets the are wired to each coil.) Sensors for throttle close completely. An air crankshaft position or camshaft passage bypassing the throttle allows position (or both) are used by both the the engine to idle. A computer ignition module and computer to fire controlled motor adjusts air flow the correct coil at the proper time. The through the bypass to set idle speed. computer provides spark advance Smaller engines can stumble or stall timing as before - by looking at vehicle at idle when the air conditioner speed, engine load and temperature. compressor turns on or the power (RPM, throttle position, coolant steering is used. To prevent this, temperature and manifold pressure or switches tell the computer when these mass air flow sensors are used.) Refer demands are coming so it can to vehicle service manual for detailed increase the idle accordingly. ignition system descriptions. 30 Computer controlled Other computer emission systems functions

• EGR (Exhaust Gas The computer often controls various Recirculation) Valve other functions around the vehicle. Detailed explanations may be found in The EGR valve lets exhaust gases re- your vehicle service manual. Some enter the intake manifold and mix with typical examples are... the incoming air/fuel. The presence of exhaust gases reduces combustion temperatures in the cylinders and this • Air Conditioner (A/C) Clutch reduces poisonous NOx emissions. The computer controls the flow of The computer can turn off the air gases through the EGR valve. The conditioner to reduce engine loading. EGR system is only used during warm This is desirable during heavy engine cruise conditions. A partially acceleration, engine cranking or low open EGR valve at other times can speed steering maneuvering. The cause stalling. Various types of EGR computer may also disable the air systems are used on different vehicles. conditioner when refrigerant pressure The EGR valve may be operated by is too low (or high) to prevent A/C engine vacuum or with a computer damage. The computer stops the air controlled electrical (or vacuum) conditioner by using a relay to signal. See “EGR” in Glossary (Section disconnect voltage from the A/C 8) for more details. clutch.

• Air Injection System • Radiator Cooling Fan The computer controls engine cooling This system reduces harmful carbon fan (electric type) operation on most monoxide (CO) and hydrocarbon (HC) vehicles. Usually the fan is turned on emissions. The computer takes outside when engine temperature exceeds a air from an air pump and directs it to certain level or when the air condition- the exhaust manifold during engine ing system is used. The computer uses warm-up. (The extra air helps partially a relay to power the fan. Some burned exhaust gases to completely vehicles have a second fan for extra burn and reduce pollution.) After cooling. warm-up, depending upon vehicle, the air pump may send air down to the catalytic convertor or “dump” it back to • Variable Assist Power Steering the atmosphere. Various types of Air Injection systems are used on different Saturn Vehicles: This system delivers vehicles. Refer to “Air Injection power steering assist based on vehicle System” in Glossary (Section 8) for speed - little assist during high speed more explanation. straight steering, increased assist for low speed turns. The computer controls fluid flow in the power steering • Fuel Evaporation Recovery pump using an Electronic Variable System Orifice (EVO) actuator (more fluid flow provides more steering assist). Refer A special canister collects vapors to “EVO” in Glossary (Section 8) for evaporating from the fuel tank, more details. preventing them from escaping into the atmosphere and causing pollution. During warm engine cruise conditions, • Torque Convertor Clutch the computer opens a connection between the cannister and the engine The computer can control the lock-up (by energizing the Purge solenoid.) clutch in an automatic transmission Then, engine vacuum draws the trapped torque convertor. The clutch is locked fuel vapors into the engine for burning. during steady, warm engine cruise 31 conditions. This improves fuel economy vehicle speed, engine loading and other by eliminating power loss in the torque sensor information to determine the convertor. The computer energizes a optimum shift performance. The solenoid to achieve lock-up. Signals computer can also set the shift quality from the engine coolant temperature, - anywhere from harsh to smooth. This throttle position and vehicle speed is done using a “force motor” actuator sensors are used. in the transmission to adjust the internal fluid line pressure. • Transmission Control Some transmissions have computer More information controlled shifting. Two solenoids mounted in the transmission are The Glossary (Section 8) describes energized singly, or in combination, to various sensors and actuators used in select a gear ratio. The solenoids computer controlled engine systems. direct the flow of fluid within the You can learn more by reading these transmission to cause the shift. The definitions. computer uses throttle position,

32 GLOSSARY

A/C solenoids and motors. Some vehicles have an Air conditioner. Actuators allow the ECM to electrically powered air control engine operation. pump controlled by the A/C Clutch ECM. This system injects A/F air into the exhaust relay Air/fuel. manifold only when the The ECM uses this relay to pump is energized and energize the A/C clutch - to Air Injection running. No air is injected turn the A/C system on or Reaction (AIR) when the pump is off. (The off. air pump does not send air system to the catalytic convertor in A/C On (A/C This is an emission control this version.) Signal) system operated by the ALDL An input signal to the ECM ECM. During cold engine indicating that either the A/ warm-up, an air pump Assembly Line Diagnostic C compressor is running or injects outside air into the Link. This is the connector that A/C operation is being exhaust manifold to help that the Code Scanner requested (depends upon burn hot exhaust gases. plugs into for testing vehicle). Then ECM This reduces pollution and purposes. The connector is adjusts idle speed to speeds warm-up of oxygen wired to the ECM, and is prevent engine stalling sensor and catalytic usually located under the when the A/C system is convertor. After the engine dashboard on the driver’s engaged. The ECM may is warm, the air will either side. also turn on the engine be “dumped” back to the cooling fan. atmosphere (or into the air BARO cleaner) or sent into the Barometric Pressure A/C Pressure catalytic convertor. There Sensor. (See MAP sensor are various versions of the for explanation.) sensor AIR system - depends This sensor is connected upon vehicle. Boost control to the A/C refrigerant line. The air pump is usually belt solenoid It measures refrigerant driven by the vehicle pressure and sends a engine. The ECM controls Used on certain voltage signal to the ECM. air flow from the pump by supercharger equipped The ECM will turn off the operating two electrically engines. This solenoid is A/C system (by de- powered solenoid valves. normally energized by the energizing the A/C Clutch An Electric Air Divert Valve ECM. (This allows the relay) to prevent either “dumps” the air to supercharger system to compressor damage if the atmosphere (valve operate normally.) The pressure is too high or low. unpowered) or sends the ECM de-energizes the solenoid during higher A/C Pressure air further into the system (valve energized). A engine speed and load switch second control valve, the conditions to reduce boost pressure. This is a mechanical switch Air Switching Valve, routs connected to the A/C the air to the catalytic Brake switch refrigerant line. The switch is convertor (valve activated (which sends a unpowered) or to the signal signal to the ECM) when the exhaust manifold (valve An input signal to the ECM A/C refrigerant pressure energized). These two indicating that the brake becomes too low. The ECM valves may be individual pedal is being depressed. will turn off the A/C system components or combined Vehicles with Cruise (by de-energizing the A/C into one assembly. Control systems monitor Clutch relay) to prevent The ECM normally sends the brake switch to compressor damage. Some air to the catalytic determine when to engage vehicles have a second convertor during warm (or disengage) the cruise switch activated when the engine operation. The ECM control function. The brake refrigerant pressure is too will divert air away from the switch may also have a high. convertor to prevent circuit supplying power to overheating damage under the Torque Convertor Actuator certain operating Clutch (TCC) solenoid. Devices which are conditions, such as decel, This connection ensures powered by the ECM to high RPM or “rich” air/fuel the TCC solenoid will control things. Actuator conditions. disengage when the brake types include relays, pedal is depressed (see TCC definition). 33 C3 Thus, closed loop operation Duty Cycle Computer Command means the ECM can “fine A term applied to Control. The name for the tune” control of a system to frequency signals - those GM electronic engine get an exact result providing which are constantly control system used on the ECM has a sensor (or switching between a small most vehicles built since other means) to check voltage value (close to 1982. results. zero) and a larger value Continuity (usually 5 volts or greater). CALPAK Duty cycle is the A “spare tire” for the ECM. An unbroken, continuous percentage of time the It is circuitry which can circuit through which an signal has a large voltage operate the vehicle fuel electric current can flow. value. For example, if the injectors in a limited CPS signal is “high” (large fashion should the ECM voltage) half of the time malfunction. The CALPAK Crankshaft Position then the duty cycle is 50%. is hidden behind an Sensor. This sensor sends If the signal is “high” only access door on the ECM. a frequency signal to the one fourth of the time, then The replaceable CALPAK ECM. It is used to the duty cycle is 25%. A module is only used on reference fuel injector duty cycle of 0% means certain ECM’s. operation and synchronize the signal is always at a spark plug firing on “low” value and not CAM distributorless ignition changing. A duty cycle of Camshaft Position Sensor. systems (DIS). 100% means the signal is This sensor sends a CTS always at a “high” value frequency signal to the and not changing. The ECM. Vehicles with Coolant Temperature engine control computer sequential fuel injection Sensor. This sensor is a uses duty cycle type (SFI) use this signal to thermistor - a resistor signals when it wants more synchronize the injector whose resistance than just “on-off” control of firing order. Some DIS decreases with increases an actuator. This is how it type ignition systems use in temperature. The sensor works: A 50% duty cycle this signal to synchronize is threaded into the engine signal going to a vacuum spark plug firing. block and contacts the switching solenoid means engine coolant. The ECM the solenoid will be “on” Closed Loop (C/L) uses this signal for control (passing full vacuum) half the time and “off” (passing This is when a control of fuel delivery, spark advance and EGR flow. no vacuum) half the time. system performs an action The average amount of (expecting a certain Digital Signal vacuum passing through result), then checks the the solenoid will be one results and corrects its An electronic signal which has only two (2) voltage half the full value because actions (if necessary) until the solenoid is only “on” for the desired results are values: a “low” value (close to zero) and a “high” value one half the time. (The achieved. Example: Fuel signal switches at a rapid delivery. The ECM (usually 5 volts or greater). Sometimes the low voltage rate, such as ten times a operates a fuel injector in second.) Thus, the a way which should deliver condition is called “Off” and the high voltage condition computer can get a an optimum air/fuel vacuum controlled actuator mixture - if everything in is called “On”. Signals which can have any to move half way between the fuel system is “no vacuum” position and operating as expected! In voltage value are called “analog” signals. “full vacuum” position. closed loop operation, the Other positions can be ECM uses the oxygen DIS achieved by changing the sensor to check the duty cycle of the control results. (Fuel delivery may Distributorless Ignition signal which in turn be different than expected System or Direct Ignition changes the average because of variations in System. A system which amount of control vacuum. fuel pressure or injector produces the ignition spark operation.) If the oxygen without the use of a DVM sensor indicates a “rich” distributor. condition, the ECM will Digital Volt Meter. An compensate by reducing Driver instrument using a numeric readout to display fuel delivery until the A transistor “switch” inside oxygen sensor signals an measured voltage values the ECM used to apply as opposed to a moving optimum air/fuel ratio. power to an external Likewise, the ECM will needle on a gauge face. device. This allows the Usually the instrument has compensate for a “lean” ECM to control relays, condition by adding fuel other measuring solenoids and small capabilities, such as until the oxygen sensor motors. once again signals an resistance and current, optimum air/fuel mixture. and may be called a DMM 34 (Digital Multi-Meter). Most backpressure to operate spark to eliminate the DVM’s have 10 Megohm the EGR valve. The ECM knock condition. input impedance. This does not control the EGR means the circuit under valve in this case, but it EST test will not be can switch off the valve Electronic Spark Timing. electronically disturbed completely when desired. An ignition system where when the DVM is (The ECM operates a the ECM controls the spark connected for a measure- solenoid switch to cut off advance timing. A signal ment. the backpressure control called EST goes from the signal to the valve.) ECM to the ignition module ECM The second system uses which fires the spark coil. Electronic Control Module. an EGR valve entirely The ECM determines The “brains” of the engine controlled by the ECM. optimum spark timing from control system. It is a This valve contains three sensor information - engine computer housed in a individual flow passages: speed and RPM, throttle metal box with a number of small flow, medium flow position, coolant sensors and actuators and large flow. Each temperature, engine load, connected with a wiring passage has an electric vehicle speed, Park/Neutral harness. Its job is to solenoid. (Passage closed switch position and knock control fuel delivery, idle when solenoid off - sensor condition. speed, spark advance passage open when timing and emission solenoid energized.) The EVO systems. The ECM ECM energizes one or Electronic Variable Orifice receives information from more solenoids in actuator. This is a solenoid sensors, then energizes combination to set up mounted in the power various actuators to control different flow rates through steering pump. It is used in the engine. The ECM is the valve as required. some variable assist power sometimes called PCM The third system is also steering systems. The (Powertrain Control directly controlled by the solenoid controls the Module) in vehicles having ECM. This EGR valve is amount of fluid passed to other computers. These vacuum operated (the the steering gear. other computers are used normally closed valve Increasing fluid flow for climate control, opens as vacuum is generates more power entertainment systems, applied). The ECM applies steering assist. The ECM etc. control vacuum to the EGR controls the solenoid by EFI valve using a solenoid using a duty cycle type connected to a vacuum signal (see “duty cycle” Electronic Fuel Injection. A source. The ECM uses a definition). The ECM uses term applied to any system duty cycle type signal to information from the where a computer controls vary the amount of vacuum vehicle speed sensor fuel delivery to an engine passing through the (VSS) and the handwheel by using fuel injectors. solenoid. (See “Duty sensor (which sends a Cycle” definition.) signal related to the rate of EGR steering wheel turning). Exhaust Gas Recirculation. EMI During low speed turns, the The EGR system Electromagnetic ECM increases the EVO recirculates exhaust gases Interference. Undesired solenoid opening to provide back into the intake signals interfering with a additional steering assist. The ECM decreases manifold to reduce NOx needed signal. For emissions. The EGR valve example: static on a radio steering assist during controls the flow of brought about by lightning straight line driving by exhaust gases back into flashes or closeness to reducing fluid flow through the intake manifold. Some high voltage power lines. the EVO solenoid. EGR valves are operated with a vacuum signal while ESC EVRV others are electrically Electronic Spark Control. Electronic Vacuum controlled. The amount of This is an ignition system Regulator Valve. This EGR valve opening function which works on actuator is controlled by determines the flow vehicles having a knock the ECM and is used to through the valve. EGR sensor mounted on the vary the amount of vacuum recirculation is only used engine block. The knock applied to a vacuum during warm engine cruise sensor is wired to circuitry operated device - usually conditions. EGR flow at in a separate module the EGR valve. other times can cause (early version) or inside the FBC stalling or no starts. There ECM (later version). If the are three types of EGR sensor detects engine Feedback Carburetor. This systems controlled by the knock, the ESC function is used on early versions of ECM. alerts the ECM which will computer controlled One system uses exhaust immediately retard the engines. It is a carburetor which can have its fuel 35 delivery modified by an activated by hydraulic Handwheel electronic signal from the pressure and may be sensor ECM. The signal controls a normally open or closed, “mixture control solenoid” depending upon vehicle. This is a three wire sensor (MCS) attached to the The ECM uses gear (power, ground and signal carburetor body. information for control of the wires). It is used in some torque convertor clutch, Variable Assist Power Frequency some emission systems and Steering systems. The The frequency of an for transmission diagnostic ECM uses the sensor electronic signal is a purposes. signal to determine how measure of how often the fast the steering wheel is signal repeats a voltage Ground being turned. Then the pattern in a one second The return path for current ECM can apply the correct time span. For example: to flow back to its source. amount of power steering suppose a signal starts at (Usually the negative assist based on vehicle zero volts, goes to five battery terminal.) It is also speed. See “EVO” volts then returns to zero the reference point from (Electronic Variable again. If this pattern which voltage measure- Orifice) actuator definition repeats itself 100 times in ments are made. That is, it for more information. one second, then the is the connection place for HEI signal frequency is 100 the minus (-) test lead from cycles per second - or 100 the voltmeter. High Energy Ignition. Hertz. Ignition system which Hall Effect pulses the spark coil by Fuel Injector sensor using transistor switches instead of mechanical An electronically controlled This sensor is a three wire flow valve. Fuel injectors breaker points. The type containing electronic electronics are in a module are connected to a circuitry. Two wires supply pressurized fuel supply. which use a reference power and ground. The signal coming from a (The pressure is created by third wire carries the a fuel pump.) No flow magnetic pick-up coil sensor signal back to the driven by the camshaft. occurs when the injector is ECM. The sensor consists off (not energized). When of a permanent magnet Hertz (Hz) the injector is powered, it and a small module opens fully allowing the fuel A term for frequency - containing a transistorized cycles per second. to flow. The ECM controls Hall Effect switch. A small fuel delivery by varying the air gap separates the IAC amount of time the injectors sensor and the magnet. are turned on. The magnetic field causes Idle Air Control. This is a device mounted on the Fuel Pump the Hall switch to turn on and send out a low voltage throttle body. It adjusts the Relay signal. If a metal strip (iron amount of air bypassing a closed throttle so that the The ECM energizes this or steel) is placed in the gap, it will block the ECM can control idle relay to apply power to the speed. The IAC is a vehicle fuel pump. For magnetic field from reaching the Hall device. stepper motor which safety reasons, the ECM moves a pintle within the removes power from the This causes the Hall switch to turn off and send a high air bypass passage. When fuel pump when ignition the ECM wants to change signals are not present. voltage signal out on the signal wire. idle speed, it will move the Fuel Pump pintle backwards, for more The metal strips (blades) air and faster idle, or it will signal are part of a cup or disk move it forward for less air This is a wire between the attached to a rotating and slower idle. (See ECM and the fuel pump component such as the Stepper Motor definition.) motor power terminal. The crankshaft or camshaft. As ECM uses this signal to the blades pass through Idle switch verify when voltage is at the sensor gap. the signal This is a switch built into voltage will switch high and the fuel pump (for the tip of the ISC (Idle diagnosing fuel pump low creating a series of Speed Control) motor problems). pulses. The ECM spindle. (See “ISC” determines the speed of definition.) During idle, the Gear switches rotation by measuring how throttle rests against the fast pulses appear. Hall ISC spindle and activates These are switches (usually Effect type sensors may be the switch. The ECM uses two) located inside certain used to measure speed automatic transmissions. this switch signal to and position of the identify closed throttle The ECM monitors the crankshaft or camshaft - switches to determine what condition, then operates for spark timing or fuel the engine in an “idle” or transmission gear is injector control. engaged. The switches are “deceleration” mode. 36 sensor measures manifold vacuum and sends a Electrical signals running This is when the control frequency or voltage signal into the ECM. These system performs an action (depends upon sensor signals come from (expecting a certain result), type) to the ECM. This sensors, switches or other but has no way of verifying gives the ECM information electronic modules. They if the desired results were on engine load for control give the ECM information achieved. Example: the of fuel delivery, spark about vehicle operation. ECM operates a fuel advance and EGR flow. injector expecting a certain amount of fuel to be Idle Speed Control. This delivered. (The ECM refers to a small electric Manifold Air Temperature assumes everything in the motor mounted on the sensor. This sensor is a fuel system is performing throttle body and controlled thermistor - a resistor as expected.) In open loop by the ECM. The ISC motor whose resistance operation, the ECM has no moves a spindle back and decreases with way of checking the actual forth. When the throttle is temperature. It is threaded amount of fuel delivered. released during idle, it rests into the intake manifold so Thus, a faulty fuel injector on this spindle. The ECM the ECM can determine or incorrect fuel pressure can control idle speed by the temperature of the can change the amount of adjusting this spindle incoming air. This is used fuel delivered and the ECM position. The ECM for fuel delivery would not know it. calculations. determines the desired idle In general, a control speed by looking at battery system operates “open voltage, coolant loop” only when there is no temperature, engine load Mixture Control Solenoid. practical way to monitor the and RPM. Used on computer results of an action. controlled vehicles having Example: Fuel delivery carburetors. Built into the during cold engine warm- This sensor is used to carburetor, it allows the up. The computer runs detect engine detonation ECM to “fine tune” fuel “open loop”because the (knocking). When spark delivery during warm oxygen sensor is not ready knock occurs, the sensor engine cruise. to send a signal. Without sends a pulsing signal. the sensor signal, the Depending upon vehicle, computer can not check this signal goes either to the A small electronic the actual amount of fuel ECM or a separate ESC assembly containing the delivered. (Electronic Spark Control) the functions of both the module. Then the spark PROM and CALPAK. It is advance is retarded to hidden behind an access Oxygen sensor. The eliminate detonation. The door on the ECM and is oxygen sensor is threaded sensor contains a replaceable. Only some into the exhaust manifold, piezoelectric element and is ECM’s have MEMCAL. directly into the stream of threaded into the engine the exhaust gases. The block. Vibrating the element ECM uses the sensor to generates the signal. Multi-Port Fuel Injection. “fine tune” fuel delivery. Special construction makes (See MPFI definition.) The sensor generates a the element only sensitive to voltage of 0.6 to 1.1 volts the engine vibrations when the exhaust gas is associated with knocking. A type of operating rich (low oxygen content). condition, such as “idle The voltage changes to 0.4 mode” or “cruise mode.” volts or less when the Mass Air Flow sensor. This exhaust gas is lean (high sensor measures the oxygen content). The amount of air entering the Multi-Port Fuel Injection. A sensor only operates after engine and sends a fuel injection system using it reaches a temperature of frequency or voltage signal one injector for each 349°C (660°F). (depends upon sensor type) cylinder. The injectors are to the ECM. The signal mounted in the intake voltage or frequency manifold. The injectors are Electrical signals sent from increases when the amount fired in groups rather than the ECM. These signals of incoming air goes up. individually. may activate relays or This gives the ECM other actuators for control information required for purposes around the control of fuel delivery and A break in the continuity of vehicle. The signals can spark advance. a circuit such that no also send information from current can flow. the ECM to other electronic modules, such as ignition Manifold Absolute or trip computer. Pressure sensor. This 37 ECM to energize relays or ture, and convert it to an Park/Neutral switch. This solenoids. electrical signal which the switch tells the ECM when ECM can understand. The the gear shift lever is in the ECM uses sensors to Park or Neutral position. A mechanical device for measure such things as Then the ECM will operate switching high current throttle position, coolant the engine in an “idle” circuits on and off. It is temperature, engine speed, mode. electronically controlled by incoming air and the like. a low current circuit. Relays allows a low power ECM signal to control a Sequential Fuel Injection high power device such as or Sequential Electronic This solenoid is located an electric cooling fan. Fuel Injection. A fuel inside certain automatic injection system using one transmissions. The ECM injector for each cylinder. uses this solenoid to vary The injectors are mounted the internal line pressure, This sensor type consists in the intake manifold. The as required, based on injectors are fired engine load condition of a permanent magnet with a coil of wire wrapped individually in the same around it. Nearby the sequence as the spark plug firing sequence. Programmable Read-Only sensor is a toothed Memory. A small, “reluctor” ring made of iron or steel. The ring is replaceable electrical Used in computer component hidden behind attached around a rotating component such as the controlled transmissions. an access door on the The solenoids (usually ECM. The PROM contains crankshaft. Whenever a tooth from the ring passes two) are located in the permanent programming transmission housing and information the ECM needs by the sensor, it attracts the magnetic field lines are controlled by the ECM. to operate a specific The ECM energizes the vehicle model. Included surrounding the magnet. As the field lines move, solenoids individually, or in are vehicle weight, engine combination, to select a and transmission type, they pass through the wire coil which generates a specific gear. (The axle ratio and other solenoids control the flow specifics. small voltage pulse (magnetic induction of hydraulic fluid to the principle). Thus, a voltage transmission shifting pulse is generated every valves.) The ECM selects Power steering switch. time a tooth passes by the the appropriate gear ratio This tells the ECM when sensor coil. The ECM and shift point based upon power steering is being determines the speed of engine operating used. The ECM can rotation by measuring how conditions. prevent stalling on a small, fast pulses appear. idling engine by watching Reluctance sensors may this switch and increasing be used for: A fault condition: an idle speed if power unwanted connection of steering is being used. Crankshaft or Camshaft – one electric circuit to speed, position (spark another causing a change timing or fuel injector in the normal current flow This device controls the control). path. flow of fuel vapors from the carbon canister to the Driveshaft – vehicle speed intake manifold. The (transmission or torque A device to convert an canister collects vapors convertor control, cooling electrical signal to evaporating from the fuel fan use, variable assist mechanical motion. It tank, preventing them from power steering and “cruise consists of a coil of wire escaping into the control”). with a movable metal rod atmosphere and causing in the center. When power pollution. During warm Wheel Speed – anti-lock is applied to the coil, the engine cruise conditions, resulting electromagnetism the ECM energizes the brake or traction control systems. moves the rod and Purge solenoid so the performs some mechanical trapped vapors are drawn action. The ECM often into the engine and uses solenoids to switch burned. Device which give the ECM information. The ECM can vacuum lines on and off. only work with electrical This allows the ECM to control vacuum operated An electrical device inside signals. The job of the sensor is to take something devices such as an EGR the ECM. It functions as the ECM needs to know, valve. Fuel injectors are four separate electronic another type of solenoid. “switches” allowing the such as engine tempera- 38 to the throttle shaft. It has a A special type of electric Torque Convertor Clutch voltage signal output which motor with a shaft that solenoid. The ECM uses increases as the the throttle rotates in small “steps” this solenoid to control the is opened. This sensor is instead of a continuous lock-up clutch in the used by the ECM for idle motion. A certain transmission torque speed, spark advance, fuel sequence of frequency convertor. (When delivery, emission system type signals is required to activated, the lock-up and automatic transmission step the motor shaft. A clutch directly connects the (electronic type) control. different signal sequence engine to the will step the shaft in the transmission.) During opposite direction. No warm engine cruise Transmission Temperature signals keeps the shaft still conditions, the ECM sensor. This sensor is a in position. A constant energizes this solenoid to thermistor - a resistor signal drive will eliminate transmission whose resistance continuously rotate the slippage and increase fuel decreases as temperature shaft. The shaft is usually economy. The ECM rises. It is mounted within connected to a threaded releases the lock-up action the transmission housing. assembly which moves when driving conditions The ECM uses this sensor back and forth to control require the transmission to to monitor transmission things such as idle speed operate as normal. operating temperature. bypass air flow (see IAC). The engine computer sends the correct signals Top Dead Center. When a Vehicle Speed Sensor. to the motor for control. piston is at its uppermost This sensor sends a position in the cylinder - frequency signal to the maximum compression. ECM. The frequency Throttle Body Injection. A increases as the vehicle fuel injection system moves faster to give the having one (or two) A resistor whose ECM vehicle speed injectors mounted in a resistance changes with information. centrally located throttle temperature. Thermistors body, as opposed to are used as sensors for positioning the injectors vehicle coolant and Wide Open Throttle. The close to an intake valve manifold air temperature. vehicle operating condition port. The resistance decreases brought about when the as temperature goes up. throttle is completely (or nearly so) open. The ECM will typically deliver extra Throttle Position Sensor. fuel to the engine at this This is a rotary type time for acceleration potentiometer connected purposes. The ECM uses the Throttle Position Sensor to identify the WOT condition.

39 ABS BASICS A General Description of ABS Systems

The following is an overview of Anti- The ABS System Lock Brake Systems (ABS). There are An ABS system combines a conven- several different types and versions. tional hydraulic braking system along Refer to vehicle service manual for with additional components including: specific details. – An ABS computer (separate from IMPORTANT: To service ABS systems the engine computer) safely and effectively, you must obtain a service manual for your vehicle and – Wheel speed sensors carefully follow all procedures. – Hydraulic control unit The computer module controls the What is ABS? ABS system. This module is called Electronic Brake Control Module ABS is a safety feature designed to (EBCM), or similar. The computer minimize accidents during braking. monitors wheel speed, acceleration When engaged, ABS stops the vehicle and deceleration using signals sent by in the shortest distance possible while the wheel speed sensors. If the giving the driver the greatest amount computer determines wheel lock-up is of steering control. likely during braking, it will control Heavy braking on non-ABS vehicles brake pressure using the Hydraulic often causes wheels to lock up. This Control Modulator. ABS components leads to a wheel skid condition and braking operation will be detailed resulting in loss of maneuverability and later in this section. As a safety a long stopping distance. The job of feature, the system reverts to normal ABS is to prevent wheel lock-up. hydraulic braking operation if the ABS computer cannot operate.

Front Wheel Master Cylinder Rear Wheel Speed Sensors Speed Sensors

Hydraulic Control Modulator

Electronic Brake Control Unit (ABS computer)

Courtesy of General Motors Corp. Typical 4-Wheel Anti-Lock Brake System 40 ABS Types wheels. The hydraulic portion is the same as the 3 Channel system. The There are three basic types... ABS computer uses a three channel • RWAL (Rear Wheel Anti-Lock) Hydraulic Control Modulator to control the right front wheel, the left front This is the simplest ABS system wheel and both rear wheels. (mostly used on small rear-wheel-drive trucks). Only the rear wheels are ABS controlled – not the front. This version ABS Components stops the vehicle in a straight line but does not allow the driver to maneuver Electronic Brake Control Module because the front wheels may lock. (EBCM) May also be called Electronic Control A single speed sensor (usually Unit (ECU), or similar. mounted in the differential) monitors driveshaft rotation. The ABS computer This is a computer module - the examines changes in shaft speed to “brains” of the ABS system. The predict rear wheel lock-up. Both rear module is located either in the brakes are operated by a single passenger compartment, or close to hydraulic channel. The ABS computer the ABS hydraulic controller in the controls rear hydraulic performance, engine area. The module monitors when necessary, using a single wheel speed sensors to determine if channel Hydraulic Control Modulator lock-up is about to occur when brakes (described later). are applied. If so, the module will operate the ABS hydraulic solenoids to • 3 Channel control brake pressure and prevent This ABS system is a higher perfor- lock-up. (This process is described mance version of the RWAL version later. Refer to “How ABS Controls just described. Used on rear wheel Brakes.”) The EBCM also performs drive vehicles, this system delivers checks of itself, and other ABS short stopping distance and maneuver- components, during vehicle operation. ing control during heavy braking. All If problems are found, the ABS system four wheels are ABS controlled. is disengaged, the dashboard warning light is energized and a diagnostic Three hydraulic braking channels are trouble code is stored in ABS computer used: right front wheel, left front wheel memory. and a single channel for both rear wheels. The ABS computer uses a Brake Light Switch three channel Hydraulic Control This is the usual switch which Modulator (described later) to operate energizes the rear brake lights when the individual brake circuits as the brake pedal is applied. The ABS necessary. computer is sometimes connected to The two rear wheels are monitored with this switch - depends upon system. a single speed sensor (usually (Note: The engine control computer mounted in the differential). This is may also be connected to this switch.) similar to the RWAL system described Some ABS systems are active before. Two more speed sensors continuously. Other types wait for the individually monitor each of the front brake light switch to close before two wheels. operating. • 4WAL (4 Wheel Anti-Lock) also Wheel Speed Sensor called “4 Channel” This is a reluctance sensor (a 2-wire This ABS system is similar to the 3 type). It consists of a permanent channel version previously described, magnet with a coil of wire wrapped but is designed for front wheel drive around it. Nearby the sensor is a vehicles. The main difference is that toothed ring made of iron or steel four speed sensors are used, instead (sometimes called a reluctor, sensor of three, to individually monitor all four ring, exciter ring, pick-up ring or tone

41 Wheel Speed Sensor Operation is usually mounted close to the master Magnet Teeth Sensor cylinder. (Some To Wire Coil ring systems combine the computer hydraulic control SN modulator and the { Air master cylinder into gap one complete unit.) Rotation The valves are connected in the brake Typical Front Sensor Typical Rear Sensor lines between the master cylinder and Axle Hub and rotor housing the wheel caliper (or assembly wheel cylinder). The Sensor ABS computer controls ring brake line pressure by operating one, or more, of these Wheel solenoid valves. (In Sensor speed Wheel ABS systems, the ring sensor speed sensor process of varying brake pressure is called “modulation.” wheel). The ring is attached to the This is why the solenoid assembly is wheel, drive axle or transmission shaft. called a “modulator.”) Whenever a tooth from the ring passes by the sensor, it attracts the magnetic Some modulator types use two field lines surrounding the magnet. As solenoid valves per brake circuit: an the field lines move, they pass through “isolation” valve and a “dump” valve. the wire coil and generate a small Other types use a special “two-stage” voltage pulse (magnetic induction solenoid per brake circuit. This “two principle). Thus, a voltage pulse is stage” solenoid provides the same generated every time a tooth passes brake fluid control as the “isolation” by the sensor coil. This voltage signal and “dump” solenoids. is sent to the ABS computer. The “isolation” and “dump” solenoids The ABS computer determines wheel have two positions: coil off and coil speed by measuring how fast pulses fully energized. The “two stage” appear. The faster the wheel spins, the solenoid has an additional position: more quickly pulses will appear. Note: coil off, coil partially energized and coil The voltage pulses get larger as the fully energized. ABS computers wheel speeds up. (The computer controlling “two stage” type solenoids ignores pulse size.) Values can range have special built-in switching circuits from a fraction of a volt (low speed) to to energize the solenoid properly. several volts (high speed). Refer to “How ABS Controls Brakes” (later in this section) for a description Hydraulic Control Modulator of how the modulator is used. This is an assembly containing solenoid operated hydraulic valves. It Accumulator and Electric Pump These two components work together. Depending upon system, their use (and construction) will differ a great deal. Hydraulic Control • Low Pressure type: Accumulator Modulator and pump only used during ABS (Typical) operation. – Accumulator acts as a reservoir. It collects hydraulic fluid “bled” from

42 brake circuit during ABS operation. ABS problems. The ABS computer (ABS relieves brake line pressure to controls the warning light. avoid wheel lock-up.) Four wheel ABS systems use two accumulators: Relays one for the rear wheel circuit and the Various relays are used by ABS - other for the front wheel circuit. depends upon system. Refer to ABS The accumulator contains a circuit schematics in vehicle service moveable diaphragm which manual. Typical relays include: separates the inside into two • ABS Power relay: Supplies power chambers. One chamber collects the to the electronic brake control module hydraulic fluid. The other side (ABS computer). Note: This relay may contains a spring pressing against have built-in diodes to protect the the diaphragm. Because of the computer against voltage surges or spring, accumulator hydraulic reverse voltage conditions. pressure is about 150 PSI. • Electric Pump relay: Used by the – The electric pump operates to ABS computer to operate the electric remove fluid from the accumulators pump. (This is the pump associated and return it to the master cylinder. with the accumulator previously – Some systems have no pump. The described.) spring driven diaphragm in the • ABS Solenoid relay: Connects accumulator pushes brake fluid back vehicle battery voltage to the solenoid into the master cylinder through a circuits in the Hydraulic Control compensation port. Module. Note: This does not turn on • High Pressure type: Accumulator the solenoids. The ABS computer and pump used for both ABS and controls individual solenoids by normal brake operation. completing each circuit as required. – Accumulator stores fluid under very Digital Ratio Adapter Controller high pressure (up to 2600 PSI). The (DRAC) accumulator contains a moveable This is a small electronic module used diaphragm which separates the on some rear wheel drive vehicles. It inside into two chambers. One works with the speed sensor mounted chamber holds the hydraulic fluid. in the differential. The DRAC receives The other side is filled with high the sensor signal, processes it, then pressure Nitrogen gas. The gas acts sends it to the ABS computer, as a very strong spring keeping the speedometer and cruise control (if hydraulic fluid under great pressure. installed). The DRAC is matched to a The pressurized fluid is used during specific rear axle ratio and tire size. normal and ABS braking. Any change to the rear axle ratio or – The electric pump is a special high tire size requires recalibrating (or pressure hydraulic type. It runs as replacing) the DRAC. needed to maintain high hydraulic pressure in the accumulator. The Lateral Acceleration Sensor pump is not controlled by the ABS This sensor is only used on Corvette computer. A pressure activated switch ABS systems. It is a small module threaded into the accumulator fitting used to monitor the amount of turns the pump on and off as required. sideways force exerted on the vehicle during a hard turn. The module sends Warning Light a voltage signal to the ABS computer. All vehicles have a red “BRAKE” light The computer uses this signal to on the dashboard to warn of problems modify ABS control of the rear brakes. in the normal braking system. Some ABS systems use this “BRAKE” light to How ABS Controls Brakes warn of ABS problems as well. Other vehicles have a separate amber Depending upon system, the ABS “ANTILOCK” dashboard light to warn of computer will either: 43 – continuously monitor wheel speed (Systems using two-stage solenoid: or... Solenoid is not energized. Hydraulic – wait for brake pedal application flow same as described above.) before monitoring wheel speed. The ABS computer controls braking ABS Braking – Pressure Maintain action when wheel speed acceleration Wheel speed signals indicate lock-up or deceleration indicates lock-up is is about to occur. ABS computer takes about to occur. first step in brake control cycle: isolate Four-Wheel Drive Vehicle Note: The wheel caliper/cylinder from master ABS computer will not allow ABS cylinder – maintain fluid pressure to braking during four-wheel drive wheel. operation. (A switch in the four-wheel drive powertrain sends a signal to the ABS computer.) The ABS computer controls brake line Isolation (Master pressure by operating one, or more, Valve Cylinder) solenoid valves in the Hydraulic CLOSED To Wheel Control Modulator. Some systems use Caliper or two solenoid valves per brake circuit: Cylinder an “isolation” valve and a “dump” valve. (Accumulator Other systems use a special “two- Dump or Reservoir) Valve stage” solenoid per brake circuit. Either CLOSED system controls brake line pressure in the same way. HYDRAULIC PRESSURE FLOW

Normal Braking (no ABS action) – Isolation valve is CLOSED (ener- ABS computer sees normal wheel gized). Pressure flow between speed changes. No ABS action is master cylinder and brake caliper/ necessary. cylinder is blocked because of closed valve. Existing pressure to wheel is maintained because From hydraulic fluid is trapped between Isolation Master isolation valve and wheel. Closed Valve Cylinder isolation valve also prevents any OPEN increases in master cylinder To Wheel pressure from reaching wheel Caliper or caliper/cylinder. Cylinder Dump – Dump valve is CLOSED (not Valve (Accumulator energized). This valve has no effect CLOSED or Reservoir) on the brake pressure when it is closed. HYDRAULIC PRESSURE FLOW (Systems using two-stage solenoid: Solenoid is partially energized. Hydraulic flow same as described – Isolation valve is OPEN (not above.) energized). Brake circuit operates normally. Hydraulic pressure from master cylinder passes through isolation valve to wheel caliper/ cylinder. – Dump valve is CLOSED (not energized). This valve has no effect on the brake pressure when it is closed. 44 ABS Braking – Pressure Decrease ABS Braking – Pressure Increase Wheel speed signals indicate lock-up is Wheel speed signals indicate absence still about to occur. ABS computer takes of lock-up condition. ABS computer next step in brake control cycle: takes last step in brake control cycle: decrease hydraulic pressure to wheel increase hydraulic pressure to wheel caliper/cylinder. caliper/cylinder.

From Isolation (Master Isolation Valve Master Cylinder) Valve Cylinder CLOSED OPEN From To Wheel Wheel Caliper or Caliper or Cylinder Cylinder Dump Dump (Accumulator Valve To or Reservoir) OPEN Accumulator Valve or Reservoir CLOSED

HYDRAULIC PRESSURE FLOW HYDRAULIC PRESSURE FLOW

– Isolation valve is CLOSED (ener- – Isolation valve is OPEN (not gized). Pressure flow between energized). Master cylinder is master cylinder and brake caliper/ reconnected to wheel caliper/cylinder. cylinder remains blocked because of Once again, hydraulic pressure from closed valve. Closed isolation valve master cylinder passes through still prevents changes in master isolation valve to wheel. cylinder pressure from reaching – Dump valve is CLOSED (not wheel caliper/cylinder. energized). This valve has no effect on – Dump valve is OPEN (energized). the brake pressure when it is closed. Hydraulic pressure to wheel caliper/ (Systems using two-stage solenoid: cylinder is reduced. The open dump Solenoid is not energized. Hydraulic valve relieves pressure by “bleeding” flow same as described above.) some fluid out of the wheel circuit. The fluid travels either: back to the The ABS system is capable of brake reservoir or to an accumulator repeating the brake cycle at a rapid - depends on system. Fluid rate - up to 15 times a second. collected in the accumulator is returned to the master cylinder. Other ABS Uses Some systems use an electric pump to move the fluid. Other systems On some vehicles, the components of ABS briefly pause the ABS brake cycle. are shared with another system: Anti-Slip Then, the spring driven diaphragm Regulation (ASR) also known as traction inside the accumulator pushes the control. This system prevents wheel slip fluid back to the master cylinder. during acceleration on slick road surfaces. (Systems using two-stage solenoid: The ASR system is controlled by a Solenoid is fully energized. Hydraulic computer module. This ASR computer is flow same as described above.) connected to the same wheel speed sensors and hydraulic control modulator used by ABS. If one drive wheel slips excessively during acceleration, power will be transferred to the other drive wheel by applying brake pressure to the slipping wheel. (The ASR computer may try to stiffen throttle movement or retard engine timing before applying brake action.) 45 ABS SAFETY General Safety Guidelines to Follow When Working on ABS Vehicles

WARNING: To avoid personal injury, DO NOT open a bleeder valve or loosen a hydraulic line while ABS is pressurized. Always follow vehicle manufacturer’s procedures to depres- surize ABS before servicing. • Always use specially designed ABS brake hoses and fittings when replacing these parts. • Always use ABS recommended brake fluids. DO NOT use silicone brake fluids in ABS systems. • Always wear approved eye protection. • Always operate the vehicle in a well ventilated area. Do not inhale exhaust gases - they are very poisonous! • Always keep yourself, tools and test equipment away from all moving or hot engine parts. • Always make sure the vehicle is in park (Automatic transmission) or neutral (manual transmission) and that the parking brake is firmly set. Block the drive wheels. • Never lay tools on vehicle battery. You may short the terminals together causing harm. • Never smoke or have open flames near vehicle. Vapors from gasoline or charging battery are highly explosive. • Never leave vehicle unattended while running tests. • Always turn ignition key OFF when connecting or disconnecting electrical components, unless otherwise instructed. • Always follow vehicle manufacturer’s warnings, cautions and service procedures.

CAUTION: Some vehicles are equipped with safety air bags, also known as Supplemental Inflatable Restraint (SIR) system. You must follow vehicle service manual cautions when working around the air bag components or wiring. If the cautions are not followed, the air bag may open up unexpectedly, resulting in personal injury.

46 IMPORTANT: Always follow vehicle service manual procedures for any ABS repairs.

• Do a thorough visual and “hands-on” • Radio transmitters can interfere with inspection first. You can often find the operation of ABS computer. Keep cause of many problems by just antenna wiring from a CB radio or looking. portable telephone away from ABS wiring • ABS systems rely on accurate wheel sensor signals. Anything which • Check ABS power circuits: interferes with the wheel sensor can –Make sure vehicle alternator and create intermittent problems or set voltage regulator are working trouble codes. Note the following: properly. –Do not mix tire sizes. Rolling –Make sure vehicle battery is fully diameter must be the same for all charged. four tires. Differently sized tires (or using a “compact” spare) can cause –Make sure all ABS fuses, fusible inaccurate wheel speed sensor links and relays are good operation. • Inspect wiring for: –Do not tap the speed sensor or toothed sensor ring. Tapping these –Contact parts can disturb their magnetic with sharp properties and upset wheel speed edges. sensor operation. Press (do not (This hammer) toothed sensor ring onto happens hub, if service is required. often.) –Do not overtighten wheel lug nuts. –Contact (Specifications are in vehicle with hot surfaces, such as exhaust service manual.) Brake drum or manifolds. rotor may bend causing inaccurate –Pinched, burned or chafed wheel speed sensor operation. insulation. –Do not coat wheel speed sensor –Proper routing and connections. parts with grease. Refer to vehicle service manual for recommended • Check electrical connectors for: material. –Corrosion on pins. –Check spacing between wheel –Bent or damaged pins. speed sensor and toothed ring, especially after servicing. Incorrect –Contacts not properly seated in spacing can cause faulty sensor housing. operation. Specifications are in –Bad wire crimps to terminals. vehicle service manual. –Check for cracked or missing teeth on the wheel speed sensor ring.

• Spinning tires (or axle) on a Inspect carefully. Note that some stationary vehicle during a service connectors use a special grease on procedure may set ABS trouble the contacts to prevent corrosion. Do codes. not wipe off! Obtain extra grease, if 47 needed, from your vehicle dealer. It is a special type for this purpose.

• Make sure any recommended system flushing has been per- formed. Corrosion or dirt in ABS valving can result in poor pedal performance.

• Some body and chassis work procedures can harm the ABS computer: – Disconnect vehicle computer modules when using electric welding equipment. – Do not expose the ABS computer to high heat for a long time (for example, during vehicle painting). Keeping temperature below 185°F (85°C) for less than 2 hours is usually safe.

48 1) Use the chart to find the ABS system used on your vehicle. 2) Refer to the page listed where you will find... • preliminary checks you need to make before reading codes, • the code reading procedure, • the procedure for erasing codes from ABS computer memory, • a list of code definitions.

Model System Page Model System Page Blazer 7 86 98 Regency 5 76 C Series Astro 7 86 Pickup Truck 7 86 Blazer 7 86 K Series Bonneville 5 76 Pickup Truck 7 86 Bonneville SSE 5 76 Sierra 7 86 C Series Pickup Truck 7 86 Delta 88 5 76 DeVille 5 76 Eldorado 6 81 Electra 5 76 Fleetwood 5 76 Jimmy 7 86 K Series Pickup Truck 7 86 Park Avenue 5 76 Reatta 6 81 Riviera 6 81 S Series (2WD) Pickup Truck 7 86 Safari 7 86 Seville 6 81 Sierra 7 86 Toronado 6 81

49 Model System Page Model System Page 98 Regency 5 76 Astro 7 or 8 See note p. 52 Astro 7 or 8 See note p. 52 Blazer 7 or 8 See note p. 52 Blazer 7 86 Bravada 8 90 Bonneville 5 76 Brougham 3 64 Bonneville SSE 5 76 C Series Pickup Truck 7 86 Brougham 2 58 Caprice 2 58 C Series Pickup Truck 7 86 Corvette 1 53 Corvette 1 53 Custom Cruiser 2 58 Delta 88 5 76 Eldorado 3 64 DeVille 5 76 G Series (RWD) Van 7 86 Eldorado 6 81 Jimmy 7 or 8 See note p. 52 Electra 5 76 K Series Fleetwood 5 76 Pickup Truck 7 86 G Series (RWD) R Series Truck 7 86 Van 7 86 Reatta 3 64 Jimmy 7 86 Riviera 3 64 K Series Pickup Truck 7 86 Roadmaster 2 58 Park Avenue 5 76 S Series Pickup Truck 7 or 8 See note p. 52 R Series Truck 7 86 Safari 7 or 8 See note p. 52 Reatta 6 81 Seville 3 64 Riviera 6 81 Sierra 7 86 S Series Pickup Truck 7 86 Sonoma 8 90 Safari 7 or 8 See note p. 52 Suburban 7 86 Seville 6 81 Syclone 8 90 Sierra 7 86 T Series Pickup Truck 7 or 8 See note p. 52 Suburban 7 86 Toronado 3 64 T Series Pickup Truck 7 86 Trofeo 3 64 Toronado 6 81 Typhoon 8 90 Trofeo 6 81 V Series Truck 7 86 V Series Truck 7 86

50 Model System Page Model System Page Astro 7 or 8 See note p. 52 Astro 8 90 Blazer 7 or 8 See note p. 52 Blazer 7 or 8 See note p. 52 Bravada 8 90 Bravada 8 90 Brougham 2 58 C Series Pickup Truck 7 or 8 See note p. 52 C Series Pickup Truck 7 or 8 See note p. 52 Eldorado 4 70 Eldorado 3 64 G Series Van 8 90 G Series (RWD) Jimmy 7 or 8 See note p. 52 Van 7 86 K Series Jimmy 7 or 8 See note p. 52 Pickup Truck 7 or 8 See note p. 52 K Series Riviera 3 64 Pickup Truck 7 or 8 See note p. 52 S Series Riviera 3 64 Pickup Truck 7 or 8 See note p. 52 S Series Safari 8 90 Pickup Truck 7 or 8 See note p. 52 Seville 4 70 Safari 7 or 8 See note p. 52 Sierra 7 or 8 See note p. 52 Seville 3 64 Sonoma 8 90 Sierra 7 or 8 See note p. 52 Suburban 7 or 8 See note p. 52 Sonoma 8 90 Syclone 8 90 Suburban 7 or 8 See note p. 52 T Series Syclone 8 90 Pickup Truck 7 or 8 See note p. 52 T Series Typhoon 8 90 Pickup Truck 7 or 8 See note p. 52 Yukon 8 90 Toronado 3 64 Trofeo 3 64 Typhoon 8 90 Yukon 8 90

51 Model System Page Astro 8 90 Blazer 7 or 8 See note below Bravada 8 90 C Series Pickup Truck 7 or 8 See note below DeVille 4 70 Eldorado 4 70 G Series Van 8 90 Jimmy 8 90 K Series Pickup Truck 7 or 8 See note below S Series Pickup Truck 7 or 8 See note below Safari 8 90 Seville 4 70 Sierra 8 90 Sonoma 8 90 Suburban 8 90 T Series Pickup Truck 7 or 8 See note below Yukon 8 90

NOTE: Two different ABS systems were available for this vehicle. Each system has a different code reading procedure. Do the following to identify which system is installed: • Examine the Electro-Hydraulic Control Unit (EHCU). This assembly has both electrical and hydraulic connections. It is installed between the master cylinder and the wheel caliper (or cylinder). –If there are 5 hydraulic connections (2 inlet, 3 outlet), then vehicle has System 8. Go to page 90. –Less than 5 hydraulic connections means vehicle has System 7. Go to page 86.

52 Complete all steps before reading trouble codes!

1) Check that all ABS system 1) Start the engine. grounds are clean and tight The brake warning lamp should come ON during engine cranking, and turn OFF shortly after the engine 2) Check power sources which starts. If it does not, check the brake supply various parts of ABS warning lamp circuit in accordance system with vehicle service manual • 1990, 1991 instructions. Corvette: –Check the AIR 2) Turn the engine OFF. Turn the fuse in BAG ignition key to the ON (RUN) the underdash position, but do not start the engine. fuse block. The anti-lock lamp should illuminate –Check the BRAKE fuse in the for about 2 seconds and then turn underdash fuse block. OFF, if no trouble codes are –Check the STOP/HAZ fuse in the currently stored, however “history” underdash fuse block. trouble codes may be stored. Proceed to Step 3 below. If the anti- –Check the fuse in the CLSTR lock lamp stays ON, trouble codes underdash fuse block. are stored. Proceed directly to –Check rust colored fusible link “J” READING ABS CODES, page 54. If on the positive junction block. the anti-lock lamp does not turn ON at all or flashes very briefly (less than 3) Check that pump motor relay, 1/2 of a second), a problem exists in EBCM relay (Electronic Brake the anti-lock lamp circuitry. See your Control Module), solenoid valve vehicle service manual. relay, and EBCM connectors are properly installed (not loose) 3) Drive the vehicle at least 20 MPH. If the anti-lock lamp turns ON, This completes the visual inspection. proceed to READING ABS CODES, Perform FUNCTIONAL CHECK before page 54. reading codes!

53 6) Plug the

Code Ca IMPORTANT: Perform all steps in r Compute r Co de R Scanner TM ead PRE-DIAGNOSTIC VISUAL INSPEC- er TION and FUNCTIONAL CHECK into the test before reading ABS codes! connector • The Code Scanner only fits ONE 1) Take Safety Precautions WAY into the test connector. • Set parking brake, block drive • The Code Scanner will not harm wheels. the vehicle computer. • Put shift lever in PARK (automatic Note: The Code Scanner does not transmission) or NEUTRAL use all of the test connector contacts. (manual transmission). This is normal. • Make sure ignition key is in OFF position. 7) Turn Ignition Key to ON Position but DO NOT START THE ENGINE 2) Have a Pencil and Paper Ready WARNING: Stay away from the radiator cooling fan! It may turn This is for writing down all the codes. on.

3) Find the 8) Get Codes from Computer the Flashing Test “Anti-Lock” Connec- Light tor • Count flashes to get trouble codes. • Service manuals call this connector (Flashes begin after a few the Assembly Line Diagnostic Link seconds.) (ALDL) connector. It may also be called the Assembly Line Commu- Code 12 looks like: nication Link (ALCL) or simply test connector. ❊ PAUSE ❊❊ • The connecter is located under the FLASH (pause) FLASH FLASH dashboard on the driver’s side. (FLASH = 1, FLASH FLASH = 2. • The connector may be in full view, Put 1 and 2 together = code 12.) or it may be recessed behind a panel opening. Code 23 looks like: • The connector may have a slip-on cover labeled “Diagnostic ❊❊ PAUSE ❊❊❊ Connector.” Remove cover for FLASH FLASH (pause) testing. Replace cover after FLASH FLASH FLASH testing. Some vehicles require this cover in place for proper operation. • Each code is flashed three (3) times before the next trouble code 4) Verify Ignition Key is OFF is sent. • After all codes are sent, the whole F O TES T F N ABS ENGINE O sequence is repeated. This continues until the ignition key is turned OFF (so you can double check your code list). 5) Put the TEST switch on ABS

54 Example of code 12 only: • A code 12 is always sent even when the computer sees no ❊ PAUSE ❊❊ problem. This tells you the computer diagnostic checks are FLASH (pause) FLASH FLASH working properly. (longer pause) • All codes are two (2) digits long. ❊ PAUSE ❊❊ 9) Turn Ignition Key OFF FLASH (pause) FLASH FLASH (longer pause) 10)Remove Code Scanner and Re- PAUSE install Connector Cover, if ❊ ❊❊ supplied FLASH (pause) FLASH FLASH The computer system is now back (even longer pause, to normal operation. then start over again)

11)Refer to ABS Code Meanings on Example of code series 12 and 24: page 57. (Bosch 2S) ❊ PAUSE ❊❊ This completes the code reading FLASH (pause) FLASH FLASH procedure. (longer pause) At this point you can either: PAUSE • Have your vehicle professionally ❊ ❊❊ serviced. Trouble codes indicate FLASH (pause) FLASH FLASH problems found by the computer. (longer pause) or, • Repair the vehicle yourself using ❊ PAUSE ❊❊ trouble codes to help pinpoint the FLASH (pause) FLASH FLASH problem. IMPORTANT: Always follow vehicle (even longer pause, service manual procedures for any then go to next code) ABS repairs! ❊❊ PAUSE ❊❊❊❊ FLASH FLASH (pause) FLASH FLASH FLASH FLASH (longer pause) ❊❊ PAUSE ❊❊❊❊ FLASH FLASH (pause) FLASH FLASH FLASH FLASH (longer pause) ❊❊ PAUSE ❊❊❊❊ FLASH FLASH (pause) FLASH FLASH FLASH FLASH

(even longer pause, then start all over from the very beginning)

55 3) Wait 15 seconds, then observe the anti-lock indicator lamp. Code 12, the “diagnostic system operational” code Erase codes from memory whenever should flash indicating that all trouble you complete a repair or to see if a codes have been erased from problem will occur again. Note: The memory. computer will automatically erase codes after several restarts (typically Turn the ignition FF ON 100) if the problem does not return. switch to the OFF O position. Proceed as follows: Remove the Code FF ON Scanner, and 1) Turn the ignition O reinstall the switch to the test OFF position. connector cover (if used on T E S T ABS ENGINE vehicle). C ar C om p ut er C o de R T e M ad er

Plug the Code Scanner (make sure the TEST switch is in the ABS position) into the test connector.

2) Turn the ignition ON switch to the ON

F position. Then... F • 1990 Corvette: O When the anti-lock lamp begins to flash codes, remove the Code Scanner from the connector for about 1 second, then reinstall the Code Scanner for about one second. Repeat this procedure 3 times within 10 seconds. Leave

Car C om the Code p ute r C o de R e ad er Scanner inserted in the connector the 3rd time.

• 1991 Corvette: When the anti-lock lamp begins to flash codes, remove the Code Scanner from the connector for about 1 second, then reinstall the Code Scanner for about 1 second. Repeat this procedure 4 times within 10 seconds. Leave the Code Scanner inserted in the connector the 4th time.

56 IMPORTANT: Always follow vehicle service manual procedures for any ABS repairs!

valve does not match the commanded position as Diagnostic System Right Rear Toothed given by the EBCM Operational. Wheel Frequency Error. (Electronic Brake Control Checks for excessively Module). dirty, or damaged toothed Right Front Wheel Speed wheel (sensor ring). Mis- Sensor circuit. Checks for matched tire sizes, or use Pump Motor or Motor open, shorted or of the temporary (mini) Relay circuit. This code intermittent condition in spare tire may set this will set if the position of the subject circuit. Vehicle code. motor relay contacts do not speed must be equal to or match the commanded greater than 4 MPH for this position of those contacts code to set. Left Rear Wheel Speed as given by the EBCM Sensor circuit. Checks for (Electronic Brake Control open, shorted or Module). There is a motor Right Front Toothed intermittent condition in monitoring circuit in the Wheel Frequency Error. subject circuit. Vehicle EBCM which will detect a Checks for excessively speed must be equal to or defective relay or pump dirty, or damaged toothed greater than 4 MPH for this motor. wheel (sensor ring). Mis- code to set. matched tire sizes, or use of the temporary (mini) Solenoid Valve Relay spare tire may set this Left Rear Toothed Wheel circuit. This code will set if code. Frequency Error. Checks the position of the valve for excessively dirty, or relay contacts do not match damaged toothed wheel the commanded position of Left Front Wheel Speed (sensor ring). Mis-matched those contacts as given by Sensor circuit. Checks for tire sizes, or use of the the EBCM (Electronic open, shorted or temporary (mini) spare tire Brake Control Module). intermittent condition in may set this code. There is a motor monitoring subject circuit. Vehicle circuit in the EBCM which speed must be equal to or will detect a defective relay greater than 4 MPH for this Right Front Solenoid or a failure in the code to set. Valve circuit. This code associated circuitry. will set if the physical position of the subject Left Front Toothed Wheel valve does not match the EBCM (Electronic Brake Frequency Error. Checks commanded position as Control Module) failure. for excessively dirty, or given by the EBCM This code will set if there is damaged toothed wheel (Electronic Brake Control an internal failure of the (sensor ring). Mis-matched Module). Electronic Brake Control tire sizes, or use of the Module. temporary (mini) spare tire may set this code. Left Front Solenoid Valve circuit. This code will set if Lateral Accelerometer the physical position of the circuit. This code will set if Right Rear Wheel Speed subject valve does not there is a short or open Sensor circuit. Checks for match the commanded circuit problem in the open, shorted or position as given by the associated circuitry. intermittent condition in EBCM (Electronic Brake subject circuit. Vehicle Control Module). speed must be equal to or Lateral Accelerometer greater than 4 MPH for this signal error. This code will code to set. Rear Wheel Solenoid set if the accelerometer Valve circuit. This code signal indicates greater will set if the physical than 0.6g for 2 minutes or position of the subject more.

57 SYSTEM 2: Bosch 2U (Version A) 1990 Brougham 1991 Caprice, Custom Cruiser, Roadmaster 1992 Brougham

Pre-Diagnostic Visual • 1990 Inspection Brougham: Complete all steps before reading –Check the trouble codes! GA-TRANS fuse in the underdash 1) Check that all ABS system fuse block. grounds are clean and tight. –Check the ABS fuse in the • 1990 Brougham: underdash fuse block. –Check the ground that is located –Check the STOP/HAZ fuse in the on the right front corner of the right underdash fuse block. fender. –Check the rust colored fusible links –Check the ground that is located on the positive junction block. near the cruise control servo on • 1991 Caprice, Custom Cruiser, the fender. Roadmaster: • 1991 Caprice, Custom Cruiser, –Check fuse number 3, 17 and 19 in Roadmaster: the main fuse block. –Check the 2 grounds that are –Check the rust colored fusible link located near the left headlight. One D on the positive junction block. is on the headlight support in front of the vapor canister, the other is • 1992 Brougham: close to the wiring harness. –Check the GA-TRANS fuse in the –Check the ground that is located underdash fuse block. near the center of the left rear –Check the ABS fuse in the quarter panel. underdash fuse block. –Check the ground that is located –Check the rust colored fusible link near the thermostat housing. E on the positive junction block. • 1992 Brougham: –Check the ground that is located 3) Check that the over-voltage relay, on the right front corner of the right ABS 6-way connector, and EBCM fender. (Electronic Brake Control Module) connectors are properly installed –Check the ground that is located (not loose). near the cruise control servo on the fender. 4) Check that the parking brake switch is functioning properly. 2) Check power sources which supply various parts of ABS This completes the visual inspection. system. Perform FUNCTIONAL CHECK before reading codes! 58 Functional Check Reading ABS Codes: Bosch 2U (Version A) Brougham 1) Start the engine. IMPORTANT: Perform all steps in The brake PRE-DIAGNOSTIC VISUAL INSPEC- warning lamp TION and FUNCTIONAL CHECK should come ON before reading ABS codes! during engine cranking, and turn 1) Take Safety Precautions OFF shortly after the engine starts. If it does not, check the brake warning • Set parking brake, block drive lamp circuit in accordance with wheels. vehicle service manual instructions. • Put shift lever in PARK (automatic 2) Turn the engine OFF. Turn the ignition transmission) or NEUTRAL key to the ON (RUN) position, but do (manual transmission). not start the engine. The anti-lock • Make sure ignition key is in OFF lamp should illuminate for about 4 position. seconds and then turn OFF, if no trouble codes are currently stored. However “history” trouble codes may 2) Have a Pencil and Paper Ready. be stored. Proceed directly to Step 3 This is for writing down all the below. If the anti-lock lamp stays ON, codes. trouble codes are stored. Proceed directly to READING ABS CODES. 3) Find the Computer Test Connector 3) Drive the vehicle at least 20 MPH. If the anti-lock lamp turns ON, proceed to READING ABS CODES.

Caprice, Custom Cruiser, Roadmaster 1) Start the engine. The brake warning lamp should come ON during engine cranking, and turn OFF shortly after • Service manuals call this connector the engine starts. If it does not, the Assembly Line Diagnostic Link check the brake warning lamp circuit (ALDL) connector. It may also be in accordance with vehicle service called the Assembly Line Commu- manual instructions. nication Link (ALCL) or simply test 2) Turn the engine OFF. Turn the ignition connector. key to the ON (RUN) position, but do • The connector is located under the not start the engine. The anti-lock dashboard on the driver’s side. lamp should illuminate for about 2 • The connector may be in full view, seconds and then turn OFF if no or it may be recessed behind a trouble codes are currently stored, panel opening. however “history” trouble codes may be stored. Proceed to Step 3 below. If • The the anti-lock lamp stays ON, trouble connector codes are stored. Proceed directly to may have a READING ABS CODES. If the anti- slip-on cover lock lamp does not turn ON at all or labeled flashes very briefly (less than 1/2 of a “Diagnostic second), a problem exists in the anti- Connector.” Remove cover for lock lamp circuitry. See your vehicle testing. Replace cover after testing. service manual. Some vehicles require this cover in place for proper operation. 3) Drive the vehicle at least 20 MPH. If the anti-lock lamp turns ON, proceed to READING ABS CODES. 59 4) Verify Ignition Key is OFF Code 12 looks like:

F O T E S T PAUSE F N ABS ENGINE ❊ ❊❊ O FLASH (pause) FLASH FLASH (FLASH = 1, FLASH FLASH = 2. Put 1 and 2 together = code 12.) 5) Put the TEST switch on ABS Code 23 looks like:

6) Plug the Code ❊❊ PAUSE ❊❊❊ Scanner into FLASH FLASH (pause) the test FLASH FLASH FLASH connector • The Code • Each code is flashed three (3) Scanner times before the next trouble code is sent. Ca only fits r Computer Code Reader

T ONE WAY M • After all codes are sent, the whole into the test sequence is repeated. This connector. continues until the ignition key is • The Code Scanner will not harm turned OFF (so you can double the vehicle computer. check your code list). Example of code 12 only: Note: The Code Scanner does not use all of the test connector contacts. This is normal. ❊ PAUSE ❊❊ FLASH (pause) FLASH FLASH 7) Turn (longer pause) Ignition Key ON to ON ❊ PAUSE ❊❊

Position but F F FLASH (pause) FLASH FLASH

DO NOT O START THE (longer pause) ENGINE PAUSE WARNING: Stay away from the ❊ ❊❊ radiator cooling fan! It may turn FLASH (pause) FLASH FLASH on. (even longer pause, then start over again) 8) Get Codes from the Flashing “Anti-Lock” Light • Count flashes to get trouble codes. (Flashes begin after a few seconds.)

60 Example of code series 12 and 24: 9) Turn Ignition Key OFF ❊ PAUSE ❊❊ FF ON FLASH (pause) FLASH FLASH O (longer pause) ❊ PAUSE ❊❊ FLASH (pause) FLASH FLASH 10)Remove Code Scanner and Re- (longer pause) install Connector Cover, if supplied ❊ PAUSE ❊❊ The computer system is now back to FLASH (pause) FLASH FLASH normal operation. (even longer pause, then go to next 11) Refer to ABS Code Meanings on code) page 63. (Bosch 2U, Version A) This completes the code reading ❊❊ PAUSE ❊❊❊❊ procedure. FLASH FLASH (pause) At this point you can either: FLASH FLASH FLASH FLASH • Have your vehicle professionally (longer pause) serviced. Trouble codes indicate problems found by the computer. ❊❊ PAUSE ❊❊❊❊ or, FLASH FLASH (pause) • Repair the vehicle yourself using FLASH FLASH FLASH FLASH trouble codes to help pinpoint the problem. (longer pause) IMPORTANT: Always follow vehicle ❊❊ PAUSE ❊❊❊❊ service manual procedures for any FLASH FLASH (pause) ABS repairs! FLASH FLASH FLASH FLASH (even longer pause, then start all over from the very beginning)

• A code 12 is always sent even when the computer sees no problem. This tells you the computer diagnostic checks are working properly. • All codes are two (2) digits long.

61 3) Remove the

Code Ca r Co mp uter Code Re

T M Scanner for ader about 1 Erase codes from memory whenever second then you complete a repair or to see if a reinstall Code problem will occur again. Note: The Scanner into the connector. Repeat computer will automatically erase this procedure 4 times within 10 codes after several restarts (typically seconds. Leave the Code Scanner 100) if the problem does not return. in s er ted in the connector after the Proceed as follows: 4th time. 1) Turn the ignition Observe the anti-lock indicator lamp. switch to the ON 4) Code 12, the “diagnostic system ON position. operational” code should flash

F

F indicating that all trouble codes have The anti-lock O lamp should been erased from memory. Wait at turn OFF after 3 least 15 seconds before turning the to 4 seconds. If it does not, a failure ignition switchOFF. Remove the still currently exists which must be Code Scanner, and reinstall the test corrected before its corresponding connector cover (if used on vehicle). trouble code will clear.

FF ON O 2) Plug the Code Scanner (make sure the TEST switch is in the ABS position) into the test connector.

Car Computer Code Reade T E S T ABS ENGINE

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62 IMPORTANT: Always follow vehicle service manual procedures for any ABS repairs!

Diagnostic System Rear Axle Speed Sensor Pump Motor or Motor Operational. This code is circuit. Checks for open, Relay circuit. This code always sent. shorted or intermittent will set if the position of the condition in subject circuit. motor relay contacts do not Vehicle speed must be match the commanded Right Front Wheel Speed equal to or greater than 4 position of those contacts Sensor circuit. Checks for MPH for this code to set. as given by the EBCM open, shorted or (Electronic Brake Control intermittent condition in Module). There is a motor subject circuit. Vehicle Rear Axle Toothed Wheel monitoring circuit in the speed must be equal to or Frequency Error. Checks EBCM which will detect a greater than 4 MPH for this for excessively dirty, or defective relay or pump code to set. damaged toothed wheel motor. (sensor ring). Mis-matched tire sizes, or use of the Right Front Toothed temporary (mini) spare tire Solenoid Valve Relay Wheel Frequency Error. may set this code. circuit. This code will set if Checks for excessively the position of the valve dirty, or damaged toothed relay contacts do not match wheel (sensor ring). Mis- Right Front Solenoid the commanded position of matched tire sizes, or use Valve circuit. This code those contacts as given by of the temporary (mini) will set if the physical the EBCM (Electronic spare tire may set this position of the subject Brake Control Module). code. valve does not match the There is a motor monitoring commanded position as circuit in the EBCM which given by the EBCM will detect a defective relay Left Front Wheel Speed (Electronic Brake Control or a failure in the Sensor circuit. Checks for Module). associated circuitry. open, shorted or intermittent condition in subject circuit. Vehicle Left Front Solenoid Valve EBCM (Electronic Brake speed must be equal to or circuit. This code will set if Control Module) failure. greater than 4 MPH for this the physical position of the This code will set if there is code to set. subject valve does not an internal failure of the match the commanded Electronic Brake Control position as given by the Module. Left Front Toothed EBCM (Electronic Brake Wheel Frequency Error. Control Module). Checks for excessively dirty, or damaged toothed wheel (sensor ring). Mis- Rear Axle Solenoid Valve matched tire sizes, or use circuit. This code will set if of the temporary (mini) the physical position of the spare tire may set this subject valve does not code. match the commanded position as given by the EBCM (Electronic Brake Control Module).

63 –Check the ABS fuse in the Complete all steps before reading underdash fuse block. trouble codes! –Check the rust colored fusible link E on the positive junction block. 1) Check that all ABS system • 1991 Eldorado, Seville: grounds are clean and tight. • 1991 Brougham, Eldorado, Reatta, –Check fuse number 7 in the Riviera, Seville, Toronado, Trofeo: interior relay center. –Check the ground that is located –Check the black and blue colored behind the right headlight. fusible links on the positive junction block. –Check the ground that is located near the parking brake pedal on • 1991 Reatta, Riviera: the left side of the dash. –Check fuse number 4 in the • 1992 Eldorado, Seville: interior relay center. –Check the ground that is located –Check the black and blue colored on the engine near the alternator. fusible links on the positive junction block. –Check the ground that is located on the rear seat brace. • 1991 Toronado, Trofeo: • 1992 Riviera, Toronado, Trofeo: –Check fuse number 18 in the underdash fuse block. –Check the ground that is located behind the right headlight. –Check the black M and blue U colored fusible links on the positive –Check the ground that is located in junction block. the right front engine compart- ment. • 1992 Eldorado, Seville: • 1993 Riviera: –Check the A1 fuse in the trunk compartment fuse block. –Check the ground that is located behind the right headlight. –Check fuse number 5 in the RIGHT MAXI fuse block. –Check the ground that is located on top of the left shroud. –Check fuse number 6 in the RIGHT MAXI fuse block. 2) Check power sources which • 1992 Riviera: supply various parts of ABS –Check fuse number 4 in the system. interior relay center. • 1991 Brougham: –Check the black and blue colored –Check the GA-TRANS fuse in the fusible links on the positive junction underdash fuse block. block.

64 • 1992 Toronado, Trofeo: –Check fuse number 18 in the 1) Start the engine. underdash fuse block. The brake –Check the black and blue colored warning lamp fusible links on the positive junction should come ON block. during engine cranking, and turn OFF shortly after • 1993 Riviera: the engine starts. If is does not, –Check fuse number 4 in the interior check the brake warning lamp relay center. circuit in accordance with the –Check fuse number 6 and 9 in the vehicle service manual instructions. underdash fuse block. –Check the black colored M and P 2) Turn the engine OFF. Turn the ignition fusible links on the positive key to the ON (RUN) position, but do junction block. not start the engine. The anti-lock lamp should illuminate for about 4 seconds and then turn OFF, if no 3) Check that all ABS/TCS connec- trouble codes are currently stored. tors, and EBCTM (Electronic However “history” trouble codes may Brake and Traction Control be stored. Proceed to Step 3 below. If Module) connectors are properly the anti-lock lamp stays ON, trouble installed (not loose). codes are stored. Proceed directly to READING ABS CODES, page 66. 4) Check that the parking brake switch is functioning properly. 3) Drive the vehicle at least 20 MPH. If the anti-lock lamp turns ON, 5) Check that the brake pressure proceed to READING ABS CODES, modulator valve ground stud is page 66. clean and tight.

6) Check the over-voltage protection relay and its connector.

This completes the visual inspection. Perform FUNCTIONAL CHECK before reading codes!

65 5) Put the TEST switch on ABS

T E S T ABS ENGINE IMPORTANT: Perform all steps in Car Computer Code Reader

PRE-DIAGNOSTIC VISUAL INSPEC- TM TION and FUNCTIONAL CHECK before reading ABS codes! 6) Plug the Code Scanner into the test 1) Take Safety Precautions the test connector • Set parking brake, block drive • The Code Scanner only fits ONE wheels. WAY into the test connector. • Put shift lever in PARK (automatic • The Code Scanner will not harm transmission) or NEUTRAL the vehicle computer. (manual transmission). Note: The Code Scanner does not • Make sure ignition key is in OFF use all of the test connector contacts. position. This is normal.

2) Have a Pencil and Paper Ready 7) Turn Ignition Key ON This is for writing down all the codes. to ON Position

F but DO NOT F

START THE O 3) Find the Computer Test Connector ENGINE • Service manuals call this connector WARNING: Stay away from the the Assembly Line Diagnostic Link radiator cooling fan! It may turn on. (ALDL) connector. It may also be called the Assembly Line Commu- 8) Get Codes from nication Link (ALCL) or simply test the Flashing connector. “Anti-Lock” Light • The connector is located under the • Count flashes to dashboard on the driver’s side. get trouble codes. (Flashes begin after a few seconds.)

Code 12 looks like: ❊ PAUSE ❊❊ FLASH (pause) FLASH FLASH • The connector may be in full view, (FLASH = 1, FLASH FLASH = 2. or it may be recessed behind a Put 1 and 2 together = code 12.) panel opening. • The connector Code 23 looks like: may have a slip-on cover PAUSE labeled ❊❊ ❊❊❊ “Diagnostic FLASH FLASH (pause) Connector.” Remove cover for FLASH FLASH FLASH testing. Replace cover after testing. • Each code is flashed three (3) times Some vehicles require this cover in before the next trouble code is sent. place for proper operation. • After all codes are sent, the whole FF ON sequence is repeated. This continues O until the ignition key is turned OFF 4) Verify Ignition Key (so you can double check your code is OFF list). 66 Example of code 12 only: • A code 12 is always sent even when the computer sees no problem. This ❊ PAUSE ❊❊ tells you the computer diagnostic checks are working properly. FLASH (pause) FLASH FLASH • All codes are two (longer pause) (2) digits long. FF ON ❊ PAUSE ❊❊ O 9) Turn Ignition Key FLASH (pause) FLASH FLASH OFF (longer pause)

PAUSE 10)Remove Code ❊ ❊❊ Scanner and FLASH (pause) FLASH FLASH Re-install Connector (even longer pause, then start over Cover, if again) supplied The computer system is now back to Example of code series 12 and 24: normal operation.

PAUSE ❊ ❊❊ 11)Refer to ABS Code Meanings on FLASH (pause) FLASH FLASH page 69 (Bosch 2U, Version B) (longer pause) This completes the code reading ❊ PAUSE ❊❊ procedure. FLASH (pause) FLASH FLASH At this point you can either: (longer pause) • Have your vehicle professionally serviced. Trouble codes indicate ❊ PAUSE ❊❊ problems found by the computer. or, FLASH (pause) FLASH FLASH • Repair the vehicle yourself using (even longer pause, then go to next trouble codes to help pinpoint the code) problem. IMPORTANT: Always follow ❊❊ PAUSE ❊❊❊❊ vehicle service manual proce- dures for any ABS repairs! FLASH FLASH (pause) FLASH FLASH FLASH FLASH (longer pause) ❊❊ PAUSE ❊❊❊❊ FLASH FLASH (pause) FLASH FLASH FLASH FLASH (longer pause) ❊❊ PAUSE ❊❊❊❊ FLASH FLASH (pause) FLASH FLASH FLASH FLASH (even longer pause, then start all over from the very beginning)

67 3) Without turning the ignition switch OFF, repeat the

sequence Car C ompute Erase codes from memory whenever outlined in r Code Reade T M you complete a repair or to see if a Step 2, 2 r problem will occur again. Note: The more times. computer will automatically erase codes after several restarts (typically 100) if the problem does not return. 4) All diagnostic trouble codes should Proceed as follows: now be cleared. Confirm this by turning the ignition switch OFF, installing the Code Scanner, and 1) Turn the ignition ON turning the ignition switch back to the switch to the ON ON position (do not start the engine).

F

position. The anti- F Code 12, the “diagnostic system lock lamp should O operational” code should be the only turn OFF after 3 to code displayed. 4 seconds. If it does not, a current failure still exists which must be corrected before its corresponding 5) Turn the ignition switch OFF. Remove trouble code will clear. the Code Scanner, and reinstall the test connector cover (if used on vehicle). 2) Plug the Code Scanner (make sure the TEST switch is in the ABS into the test connector FF ON position) O until the anti-lock lamp turns ON. Remove the Code Scanner. The anti-lock lamp will turn OFF.

T E S T ABS ENGINE Car Computer Code Reade

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68 IMPORTANT: Always follow vehicle service manual procedures for any ABS repairs!

Diagnostic System Right Rear Toothed Rear Axle Solenoid Valve Operational. This code is Wheel Frequency Error. circuit. This code will set if always sent. Checks for excessively the physical position of the dirty, or damaged toothed subject valve does not wheel (sensor ring). Mis- match the commanded position as given by the Right Front Wheel Speed matched tire sizes, or use EBCM (Electronic Brake Sensor circuit. Checks for of the temporary (mini) open, shorted or spare tire may set this Control Module). intermittent condition in code. subject circuit. Vehicle speed must be equal to or Pump Motor or Motor greater than 4 MPH for this Left Rear Wheel Speed Relay circuit. This code code to set. Sensor circuit. Checks for will set if the position of the open, shorted or motor relay contacts do not intermittent condition in match the commanded position of those contacts Right Front Toothed subject circuit. Vehicle as given by the EBCM Wheel Frequency Error. speed must be equal to or Checks for excessively greater than 4 MPH for this (Electronic Brake Control dirty, or damaged toothed code to set. Module). There is a motor wheel (sensor ring). Mis- monitoring circuit in the matched tire sizes, or use EBCM which will detect a of the temporary (mini) Left Rear Toothed Wheel defective relay or pump spare tire may set this Frequency Error. Checks motor. code. for excessively dirty, or damaged toothed wheel (sensor ring). Mis-matched Solenoid Valve Relay This code will set if Left Front Wheel Speed tire sizes, or use of the circuit. the position of the valve Sensor circuit. Checks for temporary (mini) spare tire open, shorted or may set this code. relay contacts do not match intermittent condition in the commanded position of subject circuit. Vehicle those contacts as given by speed must be equal to or Right Front Solenoid the EBCM (Electronic greater than 4 MPH for this Valve circuit. This code Brake Control Module). code to set. will set if the physical There is a motor monitoring position of the subject circuit in the EBCM which valve does not match the will detect a defective relay commanded position as or a failure in the Left Front Toothed Wheel associated circuitry. Frequency Error. Checks given by the EBCM for excessively dirty, or (Electronic Brake Control damaged toothed wheel Module). (sensor ring). Mis-matched EBCM (Electronic Brake tire sizes, or use of the Control Module) failure. temporary (mini) spare tire Left Front Solenoid Valve This code will set if there is may set this code. circuit. This code will set if an internal failure of the the physical position of the Electronic Brake Control subject valve does not Module. Right Rear Wheel Speed match the commanded Sensor circuit. Checks for position as given by the open, shorted or EBCM (Electronic Brake intermittent condition in Control Module). subject circuit. Vehicle speed must be equal to or greater than 4 MPH for this code to set.

69 3) Check that all ABS/TCS connec- tors, and EBTCM (Electronic Brake and Traction Control Complete all steps before reading Module) connectors are properly trouble codes! installed (not loose).

1) Check that all ABS system 4) Check that the parking brake grounds are clean and tight. switch is functioning properly. –Check the ground that is located on the bottom left side of the engine block, near the transaxle. 5) Check that the brake pressure modulator valve ground stud is –Check the ground that is located clean and tight. on the left rear seat brace.

This completes the visual inspection. 2) Check power sources which Perform FUNCTIONAL CHECK before supply various reading codes! parts of ABS system. –Check fuse A1 (10 amp) in the trunk compartment fuse block. This fuse provides DeVille, Eldorado, Seville switched power to the EBCM. 1) Start the engine. The anti-lock lamp –Check fuse B3 (20 amp) in the should come ON during engine engine compartment fuse block. cranking, and turn OFF shortly after This fuse provides continuous the engine starts. If... power to the brake light switch. –The lamp does NOT turn OFF after –Check fuse A3 (10 amp) in the engine start, or engine compartment fuse block. –The “ANTILOCK DISABLED” This fuse provides switched power message appears, or to the amber anti-lock indicator lamp. –The “TRACTION DISABLED” message appears, –Check fuse # 5 (50 amp) in the right MAXI fuse block. This fuse then proceed to READING ABS provides continuous power to the CODES, page 71. relays in the brake pressure modulator valve assembly. –Check the fusible links on the junction block.

70 5) Put the TEST T E S T switch on ABS ABS ENGINE IMPORTANT: Perform all steps in PRE-DIAGNOSTIC VISUAL INSPEC- 6) Plug the Code TION and FUNCTIONAL CHECK Scanner into before reading ABS codes! the test Car Computer Code Re

T connector ader M 1) Take Safety Precautions • The Code Scanner only • Set parking brake, block drive fits ONE WAY into the test wheels. connector. • Put shift lever in PARK (automatic • The Code Scanner will not harm transmission) or NEUTRAL (manual the vehicle computer. transmission). Note: The Code Scanner does not • Make sure ignition key is in OFF use all of the test connector position. contacts. This is normal.

N 2) Have a Pencil and Paper Ready 7) Turn Ignition O This is for writing down all the codes. Key to ON

F

F Position but DO O NOT START 3) Find the Computer Test Connector THE ENGINE • Service manuals call this connector WARNING: Stay away from the the Assembly Line Diagnostic Link radiator cooling fan! It may turn on. (ALDL) connector. It may also be called the Assembly Line Communi- cation Link (ALCL) or simply test 8) Get Codes from the Flashing connector. “Anti-Lock” Light • Count flashes to get trouble codes. (Flashes begin after a few seconds.)

Code 12 looks like: ❊ PAUSE ❊❊ • The connector is located under the dashboard on the driver’s side. FLASH (pause) FLASH FLASH • The connector may be in full view, (FLASH = 1, FLASH FLASH = 2. or it may be recessed behind a Put 1 and 2 together = code 12.) panel opening. • The connector Code 23 looks like: may have a slip-on cover PAUSE labeled ❊❊ ❊❊❊ “Diagnostic FLASH FLASH (pause) Connector.” Remove cover for FLASH FLASH FLASH testing. Replace cover after testing. Some vehicles require this cover in place for proper • Each code is flashed three (3) times operation. before the next trouble code is sent. FF ON O • After all codes are sent, the whole sequence is repeated. This 4) Verify Ignition continues until the ignition key is Key is OFF turned OFF (so you can double check your code list). 71 Example of code 12 only: • A code 12 is always sent even when the computer sees no ❊ PAUSE ❊❊ problem. This tells you the computer diagnostic checks are FLASH (pause) FLASH FLASH working properly. (longer pause) • All codes are two (2) digits long. ❊ PAUSE ❊❊ 9) Turn Ignition Key OFF FLASH (pause) FLASH FLASH (longer pause) 10)Remove Code Scanner and Re- PAUSE install Connector Cover, if ❊ ❊❊ supplied FLASH (pause) FLASH FLASH The computer system is now back to normal operation. (even longer pause, then start over again) 11) Refer to ABS Code Meanings on page 74 (Bosch 2U, Version C) Example of code series 12 and 24: This completes the code reading ❊ PAUSE ❊❊ procedure. FLASH (pause) FLASH FLASH At this point you can either: (longer pause) • Have your vehicle professionally PAUSE serviced. Trouble codes indicate ❊ ❊❊ problems found by the computer. FLASH (pause) FLASH FLASH or, (longer pause) • Repair the vehicle yourself using trouble codes to help pinpoint the ❊ PAUSE ❊❊ problem. FLASH (pause) FLASH FLASH IMPORTANT: Always follow vehicle service manual procedures for any ABS (even longer pause, repairs! then go to next code)

❊❊ PAUSE ❊❊❊❊ FLASH FLASH (pause) FLASH FLASH FLASH FLASH (longer pause) ❊❊ PAUSE ❊❊❊❊ FLASH FLASH (pause) FLASH FLASH FLASH FLASH (longer pause) ❊❊ PAUSE ❊❊❊❊ FLASH FLASH (pause) FLASH FLASH FLASH FLASH

(even longer pause, then start all over from the very beginning)

72 4) All diagnostic trouble codes should now be cleared. Confirm this by turning the ignition switch OFF, installing the Code Scanner, and Erase codes from memory whenever turning the ignition switch back to the you complete a repair or to see if a ON position (do not start the engine). problem will occur again. Note: The Code 12, the “diagnostic system computer will automatically erase operational” code should be the only codes after several restarts (typically code displayed. 100) if the problem does not return. 5) Turn the ignition Proceed as follows: switch OFF. FF ON O 1) Turn the ignition N Remove the switch to the ON O Code Scanner,

position. The anti- and reinstall the

F F

lock lamp should O test connector turn OFF after 3 cover (if used to 4 seconds. If it on vehicle). does not, a current failure still exists which must be corrected before its corresponding trouble code will clear.

2) Install the Code Scanner

Ca (make sure r Comput er C ode Reader the TEST TM switch is in the ABS position) into the test connector until T E S T the anti-lock lamp ABS ENGINE turns ON. Remove the Code Scanner. The anti-lock lamp will turn OFF.

3) Without turning the Car Compute

r C ignition switch ode Reader

T M OFF, repeat the sequence outlined in Step 2, 2 more times.

73 IMPORTANT: Always follow vehicle service manual procedures for any ABS repairs!

Diagnostic System Left Front Wheel Speed Left Rear Wheel Speed Operational. This code is Sensor Continuity fault. Sensor Continuity fault. always sent. Checks for open, or Checks for open, or shorted condition in subject shorted condition in subject circuit. The ignition must be circuit. The ignition must be Right Front Wheel Speed on, and the vehicle not on, and the vehicle not Sensor circuit. Checks for moving for this code to set. moving for this code to set. open, shorted or intermittent condition in subject circuit. Vehicle Right Rear Wheel Speed Right Front Solenoid speed must be equal to or Sensor circuit. Checks for Valve circuit. This code greater than 4 MPH for this open, shorted or will set if the physical code to set. intermittent condition in position of the subject subject circuit. Vehicle valve does not match the speed must be equal to or commanded position as Right Front Toothed greater than 4 MPH for this given by the EBCM Wheel Frequency Error. code to set. (Electronic Brake Control Checks for excessively Module). dirty, or damaged toothed wheel (sensor ring). Mis- Right Rear Toothed matched tire sizes, or use Wheel Frequency Error. Right Front Traction of the temporary (mini) Checks for excessively Control System Pilot spare tire may set this dirty, or damaged toothed Valve fault. This code will code. wheel (sensor ring). Mis- set if the physical position matched tire sizes, or use of the subject valve does of the temporary (mini) not match the commanded Right Front Wheel Speed spare tire may set this position as given by the Sensor Continuity fault. code. EBTCM (Electronic Brake Checks for open, or and Traction Control shorted condition in Module). subject circuit. The ignition Right Rear Wheel Speed must be on, and the Sensor Continuity fault. vehicle not moving for this Checks for open, or Left Front Solenoid Valve code to set. shorted condition in subject circuit. This code will set if circuit. The ignition must be the physical position of the on, and the vehicle not subject valve does not Left Front Wheel Speed moving for this code to set. match the commanded Sensor circuit. Checks for position as given by the open, shorted or EBCM (Electronic Brake intermittent condition in Left Rear Wheel Speed Control Module). subject circuit. Vehicle Sensor circuit. Checks for speed must be equal to or open, shorted or greater than 4 MPH for this intermittent condition in Left Front Traction code to set. subject circuit. Vehicle Control System Pilot speed must be equal to or Valve fault. This code will greater than 4 MPH for this set if the physical position Left Front Toothed Wheel code to set. of the subject valve does Frequency Error. Checks not match the commanded for excessively dirty, or position as given by the damaged toothed wheel Left Rear Toothed Wheel EBTCM (Electronic Brake (sensor ring). Mis-matched Frequency Error. Checks and Traction Control tire sizes, or use of the for excessively dirty, or Module). temporary (mini) spare tire damaged toothed wheel may set this code. (sensor ring). Mis-matched tire sizes, or use of the temporary (mini) spare tire may set this code.

74 51 61 71 Right Rear Solenoid Pump Motor or Motor EBCM or EBTCM Valve circuit. This code Relay circuit. This code (Electronic Brake Control will set if the physical will set if the position of the or Traction Control position of the subject motor relay contacts do not Module) failure. This code valve does not match the match the commanded will set if there is an internal commanded position as position of those contacts failure of the Electronic given by the EBCM as given by the EBCM Brake Control Module. (Electronic Brake Control (Electronic Brake Control Module). Module). There is a motor 73 monitoring circuit in the EBTCM (Electronic Brake 55 EBCM which will detect a and Traction Control (Vehicles with defective relay or pump Module) PWM (Pulse Traction Control) motor. Width Modulated) Signal failure (4.6 Liter engine Left Rear Solenoid Valve 63 only). This code will set if circuit. This code will set if Solenoid Valve Relay there is a desired torque the physical position of the circuit. This code will set if level signal communication subject valve does not the position of the valve failure between the EBTCM match the commanded relay contacts do not match (Electronic Brake and position as given by the the commanded position of Traction Control EBTCM (Electronic Brake those contacts as given by Module)and the PCM and Traction Control the EBCM (Electronic (Powertrain Control Module). Brake Control Module). Module). 55 There is a motor monitoring circuit in the EBCM which 83 (Vehicles without will detect a defective relay Low Brake Fluid Level Traction Control) or a failure in the (Vehicles with Traction Rear ABS Solenoid Valve associated circuitry. Control). This code will set circuit. This code will set if 67 if the brake fluid level is the physical position of the low, or there is a problem subject valve does not Brakelight Switch circuit with the brake fluid level match the commanded (Vehicles with Traction sensing system. position as given by the Control). This code will set EBCM (Electronic Brake if the brakelight switch Control Module). signal is not received.

75 1) Turn the ignition key to the ON Complete all steps before reading position, but do not start the engine. trouble codes! 2) The anti-lock lamp should illuminate 1) Check brake fluid level for at least 3 seconds. If it does not, refer to the proper diagnostic chart in the vehicle service manual. 2) Release the parking brake if it is set 3) Observe the anti-lock and brake lamps while starting the engine 3) Check all ABS (ignition key is in the cranking system fuses position). Both the anti-lock and brake lamps should be 4) Check system ON during electrical connections cranking. If they –Wheel speed sensor connectors. are not, refer to the proper diagnostic chart in the vehicle –EBCM (Electronic Brake Control service manual. Module) connectors. –System relay connectors. 4) When the engine starts, allow it to –System grounds. run for 30 seconds, and then turn it OFF for 10 seconds. This completes the visual inspection. Perform FUNCTIONAL CHECK before 5) Return the ignition key to the ON reading codes! position (do not start the engine) and wait 10 seconds. Observe the condition of the anti-lock and brake warning lamps: –If the anti-lock lamp is ON, and the brake warning lamp is OFF, proceed to READING ABS CODES, page 77. –If the anti-lock lamp is OFF, and the brake warning lamp is ON, refer to the proper diagnostic chart in the vehicle service manual.

76 –If the anti-lock lamp is ON, and the nication Link (ALCL) or simply test brake warning lamp is ON, refer to onnector. the proper diagnostic chart in the • The connector is located under the vehicle service manual. dashboard on the driver’s side. –If the anti-lock lamp is OFF, and the brake warning lamp is OFF, then this indicates normal system operation, or an intermittent problem. Intermittent trouble codes may or may not be stored.

• The connector may be in full view, or it may be recessed behind a panel. An opening in the panel allows access to recessed IMPORTANT: Perform all steps in connectors. PRE-DIAGNOSTIC VISUAL INSPEC- • The connector TION and FUNCTIONAL CHECK may have a before reading ABS codes! slip-on cover 1) Safety First! labeled • Set the parking brake. “Diagnostic Connector.” Re move cover for • Put shift lever in PARK (automatic testing. Replace cover after testing. transmission) or NEUTRAL (manual Some vehicles require this cover in transmission). place for proper operation. • Block the drive wheels.

• Make sure ignition key is in OFF FF ON position. 5) Verify Ignition O Key is OFF

2) Verify Codes are Stored • Turn the ignition key to the ON 6) Put TEST switch on ABS position, but do not start the engine.

T E S T • Wait 30 seconds. ABS ENGINE Car Comput

e r Co de Reader

T • Observe anti-lock M light...

– Light ON: 7) Plug the Code Scanner into the Codes are stored. Proceed with test connector testing. • The Code Scanner only fits ONE – Light OFF: No codes are stored. WAY into the test connector. Stop testing. • The Code Scanner will not harm • Turn ignition key OFF. the vehicle engine computer. Note: The Code Scanner does not 3) Have a Pencil and Paper Ready use all of the test connector contacts. This is for writing down all the codes. Also, one Code Scanner pin may plug into an empty test connector position. This is normal. 4) Find the Computer Test Connector 8) Turn Ignition Key to ON Position • Service manuals call this connector but DO NOT START THE ENGINE the Assembly Line Diagnostic Link WARNING: Stay away from the (ALDL) connector. It may also be radiator cooling fan! It may turn called the Assembly Line Commu- on. 77 9) Get a Trouble Code from Flashing any) will be flashed in the same “Anti-Lock” Light manner as the first code. • All codes are two (2) digits long. • Repeat this step until all trouble • Count flashes to get trouble codes. codes have been read. The ABS computer can store up to 7 trouble Flashes start codes. after about a 4 second delay. 11)Turn Ignition Key OFF FF ON – The first digit O is flashed, then... – there is a 3 second pause, then... 12)Remove Code – the second digit is flashed, Scanner and then... Re-install Connector – the anti-lock light turns ON and Cover, if stays ON. Do not count this steady supplied light as a “flash.” The computer • EXAMPLES: system is now back to normal operation. Code 12 looks like: 13)Refer to ABS Code Meanings on ❊ PAUSE ❊❊ page 79 (Teves Mark ll, Version A) FLASH (3 second pause) FLASH This completes the code reading FLASH procedure. (then light stays on.) At this point you can either: (FLASH = 1, FLASH FLASH = 2. • Have your vehicle professionally Put 1 and 2 together = code 12.) serviced. Trouble codes indicate problems found by the computer. or, Code 23 looks like: • Repair the vehicle yourself using PAUSE trouble codes to help pinpoint the ❊❊ ❊❊❊ problem. FLASH FLASH (3 second pause) IMPORTANT: Always follow FLASH FLASH FLASH vehicle service manual proce- (then light stays on.) dures for any ABS repairs!

10)Get More Codes (if any) from Flashing “Anti-Lock” Light • Do this step after first code has been flashed and anti-lock light is ON steadily. Erase codes from memory whenever • Do NOT turn ignition switch off. you complete a repair or to see if a problem will occur again. – Remove 1) IMPORTANT! - Trouble codes Code cannot be cleared until they have Car Co

Scanner from mp ut er Code been read! Refer to READING ABS Re test connec- ader TM CODES, page 77. tor. Then... 2) Drive the vehicle at a speed of – Re-install Code Scanner into test greater than 18 MPH. Trouble codes connector. should automatically clear. – The next ABS trouble code (if 78 IMPORTANT: Always follow vehicle service manual procedures for any ABS repairs!

EBCM (Electronic Brake Rear Outlet Valve. Checks Left Front Wheel Speed Control Module) Failure. for open, shorted or Sensor circuit. Checks for In most cases, this code intermittent condition in the an open, short or indicates an EBCM failure. rear outlet valve solenoid intermittent condition in Follow the appropriate and its circuitry. subject circuit. chart to check the ground circuit. Left Front Wheel Speed Right Front Wheel Speed Sensor circuit. Checks for Sensor circuit. Checks for EBCM (Electronic Brake an open, short or an open, short or Control Module) Failure. intermittent condition in intermittent condition in In most cases, this code subject circuit. subject circuit. indicates an EBCM failure. Follow the appropriate chart to check the ground Right Front Wheel Speed Right Rear Wheel Speed circuit. Sensor circuit. Checks for Sensor circuit. Checks for an open, short or an open, short or intermittent condition in intermittent condition in Main Valve. Checks for subject circuit. subject circuit. open, shorted or intermittent condition in the main valve solenoid and its Right Rear Wheel Speed Left Rear Wheel Speed circuitry. Sensor circuit. Checks for Sensor circuit. Checks for an open, short or an open, short or intermittent condition in intermittent condition in Left Front Inlet Valve. subject circuit. subject circuit. Checks for open, shorted or intermittent condition in the left front inlet valve Left Rear Wheel Speed Left Front Wheel Speed solenoid and its circuitry. Sensor circuit. Checks for Sensor Signal Missing. an open, short or Checks for missing signal intermittent condition in in the subject circuit Left Front Outlet Valve. subject circuit. Checks for open, shorted or intermittent condition in Right Front Wheel Speed the left front outlet valve Left Front Wheel Speed Sensor Signal Missing. solenoid and its circuitry. Sensor circuit. Checks for Checks for missing signal an open, short or in the subject circuit. intermittent condition in Right Front Inlet Valve. subject circuit. Checks for open, shorted Either Rear Wheel Speed or intermittent condition in Sensor Signal Missing. the right front inlet valve Right Front Wheel Speed Checks for missing signal solenoid and its circuitry. Sensor circuit. Checks for in either of the rear wheel an open, short or speed sensor circuits. intermittent condition in (Note that it is impossible Right Front Outlet Valve. subject circuit. to determine which of the Checks for open, shorted rear wheel speed circuits is or intermittent condition in causing the problem.) This the right front outlet valve Right Rear Wheel Speed code will set if the front solenoid and its circuitry. Sensor circuit. Checks for wheels spin while the rear an open, short or wheels are stationary. intermittent condition in Rear Inlet Valve. Checks subject circuit. for open, shorted or Any three Wheel Speed intermittent condition in the Sensor Signals Missing. rear inlet valve solenoid and Left Rear Wheel Speed There are missing signals its circuitry. Sensor circuit. Checks for in three (3) of the four (4) an open, short or wheel speed sensor intermittent condition in circuits. subject circuit. 79 51 56 73 Left Front Wheel Right Front Wheel Speed Right Rear Wheel Hydraulic Pressure Sensor circuit. Checks for Hydraulic Pressure Reduction fault. This an open, short or Reduction fault. This code code is the result of an intermittent condition in is the result of an incorrect incorrect response to a subject circuit. response to a hydraulic hydraulic circuit pressure circuit pressure reduction reduction command as 57 command as sent by the sent by the EBCM Right Rear Wheel Speed EBCM (Electronic Brake (Electronic Brake Control Sensor circuit. Checks for Control Module). Note: This Module). Note: This code an open, short or code may also be sent may also be sent along intermittent condition in along with Code 53, which with Code 71, which has subject circuit. has the same meaning. the same meaning. 58 74 52 Left Rear Wheel Speed Left Rear Wheel Right Front Wheel Sensor circuit. Checks for Hydraulic Pressure Hydraulic Pressure an open, short or Reduction fault. This code Reduction fault. This intermittent condition in is the result of an incorrect code is the result of an subject circuit. response to a hydraulic incorrect response to a circuit pressure reduction hydraulic circuit pressure 61 command as sent by the reduction command as Shorted Low Fluid, or EBCM (Electronic Brake sent by the EBCM Hydraulic Pressure Control Module). Note: (Electronic Brake Control Switch, or shorted ABS This code may also be sent Module). Note: This code diode, or associated along with Code 54, which may also be sent along circuitry. This code will set has the same meaning. with Code 72, which has if the low fluid switch, the 75 the same meaning. hydraulic pressure switch, 53 or the ABS diode or any of Left Front Wheel Speed the associated circuitry Sensor circuit. Checks for Right Rear Wheel exhibits a short circuit an open, short or Hydraulic Pressure condition. intermittent condition in Reduction fault. This subject circuit. code is the result of an 71 76 incorrect response to a Left Front Wheel hydraulic circuit pressure Hydraulic Pressure Right Front Wheel Speed reduction command as Reduction fault. This code Sensor circuit. Checks for sent by the EBCM is the result of an incorrect an open, short or (Electronic Brake Control response to a hydraulic intermittent condition in Module). Note: This code circuit pressure reduction subject circuit. may also be sent along command as sent by the with Code 73, which has EBCM (Electronic Brake 77 the same meaning. Control Module). Note: Right Rear Wheel Speed 54 This code may also be sent Sensor circuit. Checks for along with Code 51, which an open, short or Left Rear Wheel has the same meaning. intermittent condition in Hydraulic Pressure subject circuit Reduction fault. This 72 code is the result of an Right Front Wheel 78 incorrect response to a Hydraulic Pressure Left Rear Wheel Speed hydraulic circuit pressure Reduction fault. This code Sensor circuit. Checks for reduction command as is the result of an incorrect an open, short or sent by the EBCM response to a hydraulic intermittent condition in (Electronic Brake Control circuit pressure reduction subject circuit. Module). Note: This code command as sent by the may also be sent along EBCM (Electronic Brake with Code 74, which has Control Module). Note: the same meaning. This code may also be sent 55 along with Code 52, which has the same meaning. Left Front Wheel Speed Sensor circuit. Checks for an open, short or intermittent condition in subject circuit.

80 3) Observe the anti-lock and brake lamps while starting the engine (ignition key is in the cranking Complete all steps before reading position). Both the anti-lock and trouble codes! brake lamps should be ON during cranking. If they are not, refer to the 1) Check brake fluid level proper diagnostic chart in the vehicle service manual. 4) When the engine starts, allow it to 2) Release the parking brake if it is run for 30 seconds, and then turn it set OFF for 10 seconds. 5) Return the ignition key to the ON 3) Check all ABS position (do not start the engine) system fuses and wait 10 seconds. Observe the condition of the anti-lock and brake warning lamps: 4) Check system electrical –If the anti-lock lamp is ON, and the connections brake warning lamp is OFF, proceed to READING ABS –Wheel speed sensor connectors. CODES, page 82. –EBCM (Electronic Brake Control –If the anti-lock lamp is OFF, and the Module) brake warning lamp is ON, refer to connectors. the proper diagnostic chart in the –System relay connectors. vehicle service manual. –System grounds. –If the anti-lock lamp is ON, and the This completes the visual inspection. brake warning lamp is ON, refer to Perform FUNCTIONAL CHECK before the proper diagnostic chart in the reading codes! vehicle service manual. –If the anti-lock lamp is OFF, and the brake warning lamp is OFF, then this indicates normal system operation, or an intermittent N 1) Turn the ignition O problem. Intermittent trouble codes

key to the ON may or may not be stored.

F

F position, but do O not start the engine. 2) The anti-lock lamp should illuminate for at least 3 seconds. If it does not, refer to the proper diagnostic chart in the vehicle service manual.

81 panel. An opening in the panel I allows access to recessed connectors. IMPORTANT: Perform all steps in PRE-DIAGNOSTIC VISUAL INSPEC- • The connector may have a slip-on TION and FUNCTIONAL CHECK cover labeled “Diagnostic Connec- before reading ABS codes! tor.” Remove cover for testing. Replace cover after testing. Some vehicles require this cover in place 1) Safety First! for proper • Set the parking brake. operation. • Put shift lever in PARK (automatic transmission) or NEUTRAL 5) Verify Ignition (manual transmission). Key is OFF • Block the drive wheels. FF ON O • Make sure ignition key is in OFF 6) Put TEST switch position. on ABS

2) Verify Codes are Stored 7) Plug the Code Scanner into the • Turn the ignition key to the ON Test Connector position, but do not start the engine.

T E S T • Wait 30 seconds. ABS ENGINE Car Co mp ute r Code Read

TM • Observe anti-lock er light... – Light ON: Codes • The Code are stored. Proceed with testing. Scanner only fits ONE WAY into the – Light OFF: No codes are stored. test connector. Stop testing. • The Code Scanner will not harm • Turn ignition key OFF. the vehicle engine computer. Note: The Code Scanner does not use all of the test connector contacts. 3) Have a Pencil and Paper Ready Also, one Code Scanner pin may This is for writing down all the codes. plug into an empty test connector position. This is normal. 4) Find the Computer Test Connector • Service manuals call this connector 8) Turn Ignition ON the Assembly Line Diagnostic Link Key to ON

Position but DO F (ALDL) connector. It may also be F

called the Assembly Line Commu- NOT START THE O nication Link (ALCL) or simply test ENGINE connector. WARNING: Stay • The connector is located under the away from the radiator cooling dashboard on the driver’s side. fan! It may turn on.

9) Get a Trouble Code from Flashing “Anti- Lock” Light • All codes are two (2) digits long. • The connector may be in full view, or it may be recessed behind a 82 • Count flashes to get trouble codes. 11)Turn Ignition FF ON Flashes start after about a 4 second Key OFF O delay. – The first digit is flashed, then... 12)Remove Code – there is a 3 second pause, then... Scanner and – the second digit is flashed, then... Re-install – the anti-lock light turns ON and Connector stays ON. Do not count this steady Cover, if light as a “flash.” supplied The computer • EXAMPLES: system is now back to normal Code 12 looks like: operation.

PAUSE ❊ ❊❊ 13)Refer to ABS Code Meanings on FLASH (3 second pause) FLASH page 84 (Teves Mark ll, Version B) FLASH (then light stays on.) This completes the code reading (FLASH = 1, FLASH FLASH = 2. procedure. Put 1 and 2 together = code 12.) At this point you can either: • Have your vehicle professionally Code 23 looks like: serviced. Trouble codes indicate problems found by the computer. ❊❊ PAUSE ❊❊❊ or, • Repair the vehicle yourself using FLASH FLASH (3 second pause) trouble codes to help pinpoint the FLASH FLASH FLASH problem. (then light stays on.) IMPORTANT: Always follow vehicle service manual proce- 10)Get More Codes (if any) from dures for any ABS repairs! Flashing “Anti-Lock” Light • Do this step after first code has been flashed and anti-lock light is ON steadily. • Do NOT turn ignition switch off. – Remove Code Scanner Car Compu Erase codes from memory whenever

ter C from test ode Re

TM ader you complete a repair or to see if a connector. problem will occur again. Then... – Re-install Code Scanner into test connector. 1) IMPORTANT! - Trouble codes cannot be cleared until they have – The next ABS trouble code (if been read! Refer to READING ABS any) will be flashed in the same CODES, page 82. manner as the first code. • Repeat this step until all trouble codes have been read. The ABS 2) Drive the vehicle at a speed of computer can store up to 7 trouble greater than 20 MPH. Trouble codes codes. should automatically clear.

83 IMPORTANT: Always follow vehicle service manual procedures for any ABS repairs!

EBCM (Electronic Brake Rear Outlet Valve. Checks Left Front Wheel Speed Control Module) Failure. for open, shorted or Sensor circuit. Checks for In most cases, this code intermittent condition in the an open, short or indicates an EBCM failure. rear outlet valve solenoid intermittent condition in Follow the appropriate and its circuitry. subject circuit. chart to check the ground circuit. Left Front Wheel Speed Right Front Wheel Speed Sensor circuit. Checks for Sensor circuit. Checks for EBCM (Electronic Brake an open, short or an open, short or Control Module) Failure. intermittent condition in intermittent condition in In most cases, this code subject circuit. subject circuit. indicates an EBCM failure. Follow the appropriate chart to check the ground Right Front Wheel Speed Right Rear Wheel Speed circuit. Sensor circuit. Checks for Sensor circuit. Checks for an open, short or an open, short or intermittent condition in intermittent condition in Main Valve. Checks for subject circuit. subject circuit. open, shorted or intermittent condition in the main valve solenoid and its Right Rear Wheel Speed Left Rear Wheel Speed circuitry. Sensor circuit. Checks for Sensor circuit. Checks for an open, short or an open, short or intermittent condition in intermittent condition in Left Front Inlet Valve. subject circuit. subject circui Checks for open, shorted or intermittent condition in the left front inlet valve Left Rear Wheel Speed Left Front Wheel and One solenoid and its circuitry. Sensor circuit. Checks for (1) Rear Wheel Speed an open, short or Sensor Signal Missing. intermittent condition in Checks for missing signal Left Front Outlet Valve. subject circuit. in the subject circuits. Checks for open, shorted or intermittent condition in the left front outlet valve Left Front Wheel Speed Right Front Wheel and solenoid and its circuitry. Sensor circuit. Checks for One (1) Rear Wheel an open, short or Speed Sensor Signal intermittent condition in Missing. Checks for Right Front Inlet Valve. subject circuit. missing signal in the Checks for open, shorted subject circuits. or intermittent condition in the right front inlet valve Right Front Wheel Speed solenoid and its circuitry. Sensor circuit. Checks for Either Rear Wheel Speed an open, short or Sensor Signal Missing. intermittent condition in Checks for missing signal Right Front Outlet Valve. subject circuit. in either of the rear wheel Checks for open, shorted speed sensor circuits. or intermittent condition in (Note that it is impossible to the right front outlet valve Right Rear Wheel Speed determine which of the rear solenoid and its circuitry. Sensor circuit. Checks for wheel speed circuits is an open, short or causing the problem.) This intermittent condition in code will set if the front Rear Inlet Valve. Checks subject circuit. wheels spin while the rear for open, shorted or wheels are stationary. intermittent condition in the rear inlet valve solenoid Left Rear Wheel Speed and its circuitry. Sensor circuit. Checks for an open, short or intermittent condition in subject circuit. 84 48 54 72 Any three Wheel Speed Left Rear Wheel Right Front Wheel Sensor Signals Missing. Hydraulic Pressure Hydraulic Pressure There are missing signals Reduction fault. This Reduction fault. This code in three (3) of the four (4) code is the result of an is the result of an incorrect wheel speed sensor incorrect response to a response to a hydraulic circuits. hydraulic circuit pressure circuit pressure reduction reduction command as command as sent by the 51 sent by the EBCM EBCM (Electronic Brake Left Front Wheel (Electronic Brake Control Control Module). Note: Hydraulic Pressure Module). Note: This code This code may also be sent Reduction fault. This may also be sent along along with Code 52, which code is the result of an with Code 74, which has has the same meaning. incorrect response to a the same meaning. hydraulic circuit pressure 73 reduction command as 61 Right Rear Wheel sent by the EBCM Shorted Low Fluid, or Hydraulic Pressure (Electronic Brake Control Hydraulic Pressure Reduction fault. This code Module). Note: This code Switch, or shorted ABS is the result of an incorrect may also be sent along diode, or associated response to a hydraulic with Code 71, which has circuitry. This code will set circuit pressure reduction the same meaning. if the low fluid switch, the command as sent by the hydraulic pressure switch, EBCM (Electronic Brake 52 or the ABS diode or any of Control Module). Note: Right Front Wheel the associated circuitry This code may also be sent Hydraulic Pressure exhibits a short circuit along with Code 53, which Reduction fault. This condition. has the same meaning. code is the result of an incorrect response to a 71 74 hydraulic circuit pressure Left Front Wheel Left Rear Wheel reduction command as Hydraulic Pressure Hydraulic Pressure sent by the EBCM Reduction fault. This Reduction fault. This code (Electronic Brake Control code is the result of an is the result of an incorrect Module). Note: This code incorrect response to a response to a hydraulic may also be sent along hydraulic circuit pressure circuit pressure reduction with Code 72, which has reduction command as command as sent by the the same meaning. sent by the EBCM EBCM (Electronic Brake (Electronic Brake Control Control Module). Note: This 53 Module). Note: This code code may also be sent Right Rear Wheel may also be sent along along with Code 54, which Hydraulic Pressure with Code 51, which has has the same meaning. Reduction fault. This the same meaning. code is the result of an incorrect response to a hydraulic circuit pressure reduction command as sent by the EBCM (Electronic Brake Control Module). Note: This code may also be sent along with Code 73, which has the same meaning.

85 – Do this additional check: Step on the service brake. If the brake Complete all steps before reading warning light comes ON, there is a trouble codes! problem with the combination valve. 1) Block the wheels, and release the (This valve is part of the normal parking brake. Do not step on the braking system, not part of the anti- service brake! lock braking system.) Release the 2) Turn the ignition service brake. key to the ON • If the brake light turns ON and stays position, but do not ON (or turns ON after the bulb start the engine. check), proceed to the diagnostic Observe the procedure outlined in your vehicle instrument panel brake warning light: service manual for the brake light • If the brake light turns ON, and then ON symptom. OFF after about 2 seconds, the • If the brake light stays OFF, self-diagnostic circuitry has found proceed to the diagnostic proce- NO current problems with the ABS dure outlined in your vehicle system. service manual for the brake light – DO NOT perform ABS code OFF symptom. reading procedure! A false code 9 • If the brake light is FLASHING, will be stored in ABS computer proceed to READING ABS memory if the code reading steps CODES, page 87. are followed when no faults F 3) Turn the ignition key F ON currently exist. (This is a quirk of the O to the OFF position. RWAL ABS system.)

86 IMPORTANT: Perform all steps in DIAGNOSTIC CIRCUIT CHECK before reading ABS codes! • The connector may be in full view, 1) Take Safety Precautions or it may be recessed behind a panel opening. • Set parking brake, block drive wheels. • The connector may have a • Put shift lever in PARK (automatic slip-on cover transmission) or NEUTRAL labeled (manual transmission). “Diagnostic • Make sure ignition key is in OFF Connector.” position. Remove cover for testing. Replace cover after testing. Some vehicles require this cover in place for proper 2) Verify ABS Problem Currently operation. Exists • Turn the ignition key to the ON ON position, but do not start the 4) Verify Ignition

Key is ON and F

engine. F

Engine is OFF O WARNING: Stay away from the radiator cooling fan! It may turn on. 5) Put the TEST switch on ABS

• Wait 5 seconds, and then observe T E S T the brake warning light. ABS ENGINE Ca r Computer

Code Reader – Brake light OFF: ABS computer TM does NOT detect a current problem. Do not proceed with this test! A false code 9 will be stored 6) Plug the Code Scanner into the in ABS computer memory if the Test Connector code reading steps are followed • The Code Scanner only fits ONE when no faults currently exist! Turn WAY into the test connector. the ignition key OFF and stop testing. • The Code Scanner will not harm the vehicle computer. – Brake light ON: An ABS problem currently exists. At least one trouble Note: The Code Scanner does not code is stored in computer memory. use all of the test connector Go to step 3 and continue code contacts. This is normal. reading procedure. 7) Get the Code from the Flashing 3) Find the Computer Test Connector “Brake” Light • Service manuals call this connector • Count flashes to get the trouble the Assembly Line Diagnostic Link code. (ALDL) connector. It may also be – Flashes begin after 20 seconds, called the Assembly Line Communi- or more. cation Link (ALCL) or simply test – The code starts with one long flash connector. and is followed by several short • The connector is located under the flashes. Count the long flash along dashboard on the driver’s side. with the short flashes to get the code number. After a pause, the code is repeated. 87 Code 3 looks like: vehicle service manual proce- dures for any ABS repairs! L O N G SHORT SHORT ❊ ❊ ❊ FLASH FLASH FLASH starts over Code 3 pause NOTE (multiple trouble code storage): This ABS system is only capable of Code 5 looks like: displaying one code at a time. Repair the failure which generated the L O N G SHORT SHORT SHORT SHORT displayed trouble code, and then repeat ❊ ❊ ❊ ❊ ❊ the READING ABS CODES procedure FLASH FLASH FLASH FLASH FLASH to see if any more codes are stored. starts over Code 5 pause Continue repeating the procedure until all codes are displayed, diagnosed, and • The same code is flashed over and repaired. over again. Note that the long flash helps you tell when the code is being repeated. • Important: The code may be flashed incorrectly the first time. The code will be flashed correctly the rest of the time. Count the flash Erase codes from memory when you sequences a few times to verify the complete all repairs or to see if a code. problem will occur again. • Code flashing continues until the Proceed as follows: ignition key is turned OFF or the Code Scanner is unplugged. 1) Turn the ignition FF ON key to the OFF O position. FF ON 8) Turn Ignition Key O 2) Remove the OFF indicated fuse from the fuse block and wait at least 10 seconds. 9) Remove Code Scanner and Re- install Connec- tor Cover, if supplied The computer system is now back to normal • 1988–93 C & K Trucks: operation. Remove the STOP/HAZ fuse. • 1989–92 Astro/Safari: 10)Refer to ABS Code Meanings on Remove the HORN/DM fuse. page 89 (Kelsey-Hayes RWAL) • 1989 S Series Trucks: This completes the code reading Remove the ECM B fuse. procedure. • 1990–92 G Series RWD Vans: At this point you can either: Remove the TAIL LPS fuse. • Have your vehicle professionally • 1990–91 R & V Series (Suburbans serviced. Trouble codes indicate etc.): problems found by the computer. Remove the STOP/HAZ fuse. or, • 1990–93 S & T Series Trucks: • Repair the vehicle yourself using Remove the ECM B fuse. trouble codes to help pinpoint the problem. 3) Replace fuse. Trouble codes are IMPORTANT: Always follow 88 now erased from computer memory! IMPORTANT: Always follow vehicle service manual procedures for any ABS repairs!

ECM (Electronic Control Erratic Vehicle Speed Stop (Brake) Light circuit. Module) Failure. This Sensor signal. This code This code indicates a code indicates an anti-lock indicates either a defective missing stop light signal brake system control or erratic vehicle speed from the stop light switch. module failure, or a mis- sensor (check for engine The stop light switch may read code. diagnostic trouble code be mis-adjusted or 24), defective DRAC defective, or there may be (Digital Ratio Adapter a problem with its Open Isolation valve or Controller) or its circuitry, associated wiring. defective ECM or any associated wiring. (Electronic Control An open battery feed fuse Module). This code to the ABS electronic ECM (Electronic Control indicates an open circuit in control module could also Module) Failure. This code the isolation valve or cause this code to set. indicates an anti-lock brake associated wiring. The anti- system control module lock brake system control failure, or a mis-read code. module may also have Shorted Isolation valve failed. or defective ECM (Electronic Control ECM (Electronic Control Module). This code Module) Failure. This code Open Dump valve or indicates a shorted circuit indicates an anti-lock brake defective ECM in the isolation valve or system control module (Electronic Control associated wiring. The anti- failure, or a mis-read code. Module). This code lock brake system control indicates an open circuit in module may also have failed. the dump valve or ECM (Electronic Control associated wiring. The anti- Module) Failure. This code lock brake system control indicates an anti-lock brake module may also have Shorted Dump valve or system control module failed. defective ECM failure. (Electronic Control Module). This code indicates a shorted circuit Grounded anti-lock valve ECM (Electronic Control in the dump valve or Reset Switch. This code Module) Failure. This code indicates a grounded circuit associated wiring. The anti- indicates an anti-lock brake in the anti-lock valve reset lock brake system control system control module switch or associated wiring module may also have failure. failed.

Excessive actuation of ECM (Electronic Control the Dump valve during Open circuit to the Module) Failure. This code an anti-lock stop. On 2 Vehicle Speed Sensor indicates an anti-lock brake wheel drive vehicles, this signal. This code indicates system control module code indicates probable a defective vehicle speed failure. failure of the isolation/dump sensor (check for engine valve assembly. On 4 diagnostic trouble code wheel drive vehicles, this 24), defective DRAC code indicates either (Digital Ratio Adapter possible failure of the Controller) or its circuitry, isolation/dump valve or any of its associated assembly, or a failure in wiring. An open battery the front axle transfer case feed fuse to the ABS switch or its associated electronic control module wiring and/or connectors. could also cause this code to set.

89 diagnostic procedure outlined in Complete all steps before reading your vehicle service manual for the trouble codes! anti-lock light ON symptom. • If the anti-lock light stays OFF, proceed to the diagnostic proce- 1) Block the wheels, and release the dure outlined in your vehicle parking brake. Do not step on the service manual for the anti-lock service brake! light OFF symptom.

2) Turn the ignition key to the ON 3) Turn the ignition position, but do not start the engine. FF ON key to the OFF O Observe the instrument panel amber position. Proceed anti-lock light: to READING • If the anti-lock ABS CODES, light turns page 91. ON, and then OFF after about 2 seconds, the diagnostic circuit check is successful. Proceed to Step 3. • If the anti-lock light turns ON and stays ON, or turns ON after the bulb check, proceed to the 90 4) Verify Ignition Key is OFF

TES T ABS ENGINE FF ON IMPORTANT: Perform all steps in O DIAGNOSTIC CIRCUIT CHECK before reading ABS codes! Note (1990, 1991 only): Codes 21, 22, 25, 26, 31, 32, 35, and 36 will disable ABS system, but are not stored in 5) Put the TEST switch on ABS computer memory. They are erased when ignition is turned off. All other codes are stored in memory when they 6) Plug the Code

C Scanner into ar C om occur. pu te r C od e R T ea M the Test de r 1) Take Safety Precautions Connector • Set parking brake, block drive • The Code wheels. Scanner only fits ONE WAY into the • Put shift lever in PARK (automatic test connector. transmission) or NEUTRAL (manual • The Code Scanner will not harm transmission). the vehicle computer. • Make sure ignition key is in OFF Note: The Code Scanner does not position. use all of the test connector contacts. This is normal. 2) Have a Pencil and Paper Ready This is for writing down all the codes. 7) Turn Ignition ON Key to ON

F

Position but DO F 3) Find the Computer Test Connector NOT START THE O • Service manuals call this connector ENGINE the Assembly Line Diagnostic Link WARNING: Stay away from the (ALDL) connector. It may also be radiator cooling fan! It may turn called the Assembly Line Communi- on. cation Link (ALCL) or simply test connector. • The connector is located under the 8) Get Codes from the Flashing dashboard on the driver’s side. “Anti-Lock” Light • Count flashes to get trouble codes. (Flashes begin after a few seconds.)

Code 12 looks like:

PAUSE • The connector may be in full view, ❊ ❊❊ or it may be recessed behind a FLASH (pause) FLASH FLASH panel opening. (FLASH = 1, FLASH FLASH = 2. • The connector Put 1 and 2 together = code 12.) may have a slip- on cover labeled “Diagnostic Code 23 looks like: Connector.” Remove cover for testing. Replace ❊❊ PAUSE ❊❊❊ cover after testing. Some vehicles require this cover in place for proper FLASH FLASH (pause) operation. FLASH FLASH FLASH 91 • After all codes are sent, the whole position. T E S T ABS ENGINE sequence is repeated. This 2) Put the Code continues until the ignition key is Scanner TEST turned OFF (so you can double switch in the ABS check your code list). position. • All codes are two (2) digits long. 3) Plug the Code Scanner into the

9) Turn Ignition Key OFF test connector Car C omp ut er Co de R

T ea M for 2 seconds. der Remove the FF ON O Code Scanner for 2 seconds. Repeat this procedure 5 more times. Important: A false code 65 may be 10)Remove Code Scanner and Re- created if the plug/unplug procedure install Connector Cover, if is only done twice. You must supplied complete all of step 3 in order to erase The computer system is now back to FF ON trouble codes. O normal operation. 4) Turn the ignition switch to the 11) Refer to ABS Code Meanings on OFF position. Reinstall test connector page 93 (Kelsey-Hayes 4WAL) cover (if used on vehicle).

This completes the code reading ON procedure. • 1992 and newer:

F F

At this point you can either: 1) Turn the ignition O switch to the ON • Have your vehicle professionally position.

serviced. Trouble codes indicate T E S T problems found by the computer. 2) Put the Code ABS ENGINE or, Scanner TEST switch in the • Repair the vehicle yourself using ABS position. trouble codes to help pinpoint the

Car C problem. Plug the Code omp 3) uter Co de R

ea TM IMPORTANT: Always follow Scanner into the der vehicle service manual proce- test connector dures for any ABS repairs! for 2 seconds. Remove the Code Scanner for 1 second . Repeat this procedure once more. Trouble codes are erased when the anti-lock and brake lights turn on, then turn off. Repeat the plug/unplug procedure if necessary.

4) Turn the ignition

Erase codes from memory whenever switch to the OFF FF ON O you complete a repair or to see if a position. Reinstall test problem will occur again. connector cover (if Proceed as follows: used on vehicle). ON • 1990, 1991:

F F

1) Turn the ignition O switch to the ON 92 IMPORTANT: Always follow vehicle service manual procedures for any ABS repairs! the diagnostic chart for be out of specification, or there diagnostic trouble code 81. may be loose, corroded, or ABS System functional, dirty connections in this circuit. 2WD, service brake not applied. This code indicates that the anti-lock brake Right Front Wheel Speed system as installed on a 2 Sensor Circuit resistance Left Front Wheel Speed wheel drive vehicle is is incorrect. This code is Sensor Voltage Output is functioning normally. As indicative of high resistance incorrect. This code indicated above, this code in this particular wheel indicates a problem in the should appear without the speed sensor circuit. The wheel speed sensor or its service brakes applied. resistance of the wheel associated tone (toothed) speed sensor may be out of wheel. Check for the proper specification, or there may air gap between the wheel be loose, corroded, or dirty speed sensor and tone ABS System functional, connections in this circuit. wheel, missing or broken 2WD, service brake teeth on the tone wheel, a applied. This code indicates loose, improperly mounted, that the anti-lock brake or mis-adjusted wheel system as installed on a 2 Right Front Wheel Speed Sensor Voltage Output is speed sensor. An wheel drive vehicle is intermittent connection in functioning normally. As incorrect. This code indicates a problem in the the associated wiring can indicated above, this code also set this code. should appear with the wheel speed sensor or its service brakes applied. If, associated tone (toothed) with the service brakes wheel. Check for the proper applied, the anti-lock lamp air gap between the wheel Left Front Wheel Speed continues to indicate a code speed sensor and tone Sensor Voltage Output is 12, it is likely that there is a wheel, missing or broken erratic. Erratic voltage output problem with the stop (brake) teeth on the tone wheel, a usually indicates a loose, lamp switch circuit. loose, improperly mounted, dirty, or corroded connection. Assistance is available under or mis-adjusted wheel speed Check the connections at the the diagnostic chart for sensor. An intermittent wheel speed sensor diagnostic trouble code 81. connection in the associated connector, the wheel speed wiring can also set this code. sensor harness, and the EHCU (Electro-Hydraulic Control Unit). There may also ABS System functional, be a problem in the wheel 4WD, service brake not Right Front Wheel Speed Sensor Voltage Output is speed sensor or its applied. This code indicates associated tone (toothed) that the anti-lock brake erratic. Erratic voltage output usually indicates a loose, dirty, wheel. Check for the proper system as installed on a 4 air gap between the wheel wheel drive vehicle is or corroded connection. Check the connections at the wheel speed sensor and tone functioning normally. As wheel, missing or broken indicated above, this code speed sensor connector, the wheel speed sensor harness, teeth on the tone wheel, a should appear without the loose, improperly mounted, service brakes applied. and the EHCU (Electro- Hydraulic Control Unit). There or mis-adjusted wheel speed may also be a problem in the sensor. wheel speed sensor or its ABS System functional, associated tone (toothed) 4WD, service brake wheel. Check for the proper One or Two Wheel Speed applied. This code indicates air gap between the wheel that the anti-lock brake Sensor Voltage Output speed sensor and tone wheel, Signals are erratic. system as installed on a 4 missing or broken teeth on the Trouble codes 23, 27, 33, wheel drive vehicle is tone wheel, a loose, or 37 may be set along with functioning normally. As improperly mounted, or mis- code 28. If one or more of indicated above, this code adjusted wheel speed sensor. these 4 codes are present, should appear with the use that code(s) to service brakes applied. If, diagnose the failure. If with the service brakes Left Front Wheel Speed trouble code 28 is the only applied, the anti-lock lamp code set, it is advisable to continues to indicate a code Sensor Circuit resistance is incorrect. This code is drive the vehicle an 14, it is likely that there is a additional period of time problem with the stop (brake) indicative of high resistance in this particular wheel speed until one of the 4 listed lamp switch circuit. codes does set, and then Assistance is available under sensor circuit. The resistance of the wheel speed sensor may use that code chart for 93 diagnosis. If code 28 Check for the proper air usually accompanied with persists as the only trouble gap between the wheel code 23, 27, 33, or 37. If it is code, it indicates that an speed sensor and tone accompanied with one or intermittent connection wheel, missing or broken more of the listed codes, use exists somewhere in the teeth on the tone wheel, a the trouble chart for that system. All connections will loose, improperly mounted, code to diagnose the have to be checked. or mis-adjusted wheel system. If trouble code 38 speed sensor appears by itself, all connections between the All Wheel Speed Sensor wheel speed sensors and the Voltage Output Signals Left Rear Wheel Speed EHCU (Electro-Hydraulic are erratic. Trouble code Sensor Circuit resistance Control Unit) will need to be 29 is usually caused by an is incorrect. This code is checked for looseness, dirt, improperly seated 8 way indicative of high resistance corrosion, etc connector at the EHCU in this particular wheel (Electro-Hydraulic Control speed sensor circuit. The Unit). Check for corrosion resistance of the wheel Right Front Isolation Valve or dirty contacts, and that speed sensor may be out of Solenoid, open circuit. the connector is properly specification, or there may Double check to make sure installed in the EHCU. be loose, corroded, or dirty that the code has been connections in this circuit. properly read. If it has, clear all trouble codes by following Right Rear Wheel Speed the ERASING ABS CODES Sensor Circuit resistance Left Rear Wheel Speed FROM COMPUTER is incorrect. This code is Sensor Voltage Output is MEMORY procedure on indicative of high resistance incorrect. This code page 88. Thoroughly road in this particular wheel indicates a problem in the test the vehicle. Check for speed sensor circuit. The wheel speed sensor or its trouble codes again. If this resistance of the wheel associated tone (toothed) code returns, the EHCU speed sensor may be out of wheel. Check for the proper (Electro-Hydraulic Control specification, or there may air gap between the wheel Unit) is defective and should be loose, corroded, or dirty speed sensor and tone be replaced. The EHCU is a connections in this circuit. wheel, missing or broken costly part! Your dealer may teeth on the tone wheel, a offer an exchange policy in loose, improperly mounted, which case your defective Right Rear Wheel Speed or mis-adjusted wheel speed unit has value (core credit) Sensor Voltage Output is sensor. An intermittent towards the purchase of the incorrect. This code connection in the associated replacement. Securely indicates a problem in the wiring can also set this attach a tag to your defective wheel speed sensor or its code. unit clearly indicating the associated tone (toothed) trouble code(s) reported by wheel. Check for the proper the defective EHCU. air gap between the wheel Left Rear Wheel Speed speed sensor and tone Sensor Voltage Output is wheel, missing or broken erratic. Erratic voltage Right Front Pulse Width teeth on the tone wheel, a output usually indicates a Modulation Valve loose, improperly mounted, loose, dirty, or corroded Solenoid, open circuit. or mis-adjusted wheel connection. Check the Refer to the explanation speed sensor. An connections at the wheel under trouble code 41. intermittent connection in speed sensor connector, the the associated wiring can wheel speed sensor also set this code. harness, and the EHCU Right Front Isolation Valve (Electro-Hydraulic Control Solenoid, short circuit. Unit). There may also be a Double check to make sure Right Rear Wheel Speed problem in the wheel speed that the code has been Sensor Voltage Output is sensor or its associated properly read. Carefully erratic. Erratic voltage tone (toothed) wheel. Check check all power and ground output usually indicates a for the proper air gap connections at the EHCU. If loose, dirty, or corroded between the wheel speed the code has been properly connection.Check the sensor and tone wheel, read, and there are no connections at the wheel missing or broken teeth on problems in the power or speed sensor connector, the tone wheel, a loose, ground circuits, clear all the wheel speed sensor improperly mounted, or mis- trouble codes by following harness, and the EHCU adjusted wheel speed the ERASING ABS CODES (Electro-Hydraulic Control sensor. FROM COMPUTER Unit). There may also be a MEMORY procedure on problem in the wheel speed page 88. Thoroughly road sensor or its associated Speed Sensor Voltage test the vehicle. Check for tone (toothed) wheel. Signal Output is erratic. trouble codes again. If this When this code appears, it is code returns, the EHCU 94 (Electro-Hydraulic Control Modulation Valve Unit). Carefully check all Unit) is defective and should Solenoid, open circuit. power and ground be replaced. The EHCU is a Refer to the explanation connections at the EHCU. costly part! Your dealer may under trouble code 41. offer an exchange policy in 71 which case your defective 53 EHCU (Electro-Hydraulic unit has value (core credit) Rear Isolation Valve Control Unit) has a RAM towards the purchase of the Solenoid, short circuit. (Random Access replacement. Securely Refer to the explanation Memory) error. Refer to attach a tag to your under trouble code 43. the explanation under defective unit clearly trouble code 41. indicating the trouble 54 code(s) reported by the Rear Pulse Width 72 defective EHCU. Modulation Valve EHCU (Electro-Hydraulic 43, 44, 47, 48, Solenoid, short circuit. Control Unit) has a ROM Refer to the explanation (Read Only Memory) 53, 54, & 68 all under trouble code 43. error. Refer to the at the same 61 explanation under trouble time. code 41. Right Front Reset Switch, If all of these codes appear open circuit. Refer to the 73 simultaneously, carefully explanation under trouble EHCU (Electro-Hydraulic check all power and ground code 41. Control Unit) has an connections at the EHCU internal circuit error. (Electro-Hydraulic Control 62 Refer to the explanation Unit). Left Front Reset Switch, under trouble code 41. 44 open circuit. Refer to the explanation under trouble 74 Right Front Pulse Width code 41. EHCU (Electro-Hydraulic Modulation Valve Control Unit) has an Solenoid, short circuit. 63 internal circuit error Refer to the explanation Rear Reset Switch, open which is causing under trouble code 43. circuit. Refer to the excessive isolation time. 45 explanation under trouble Refer to the explanation code 41. under trouble code 41. Left Front Isolation Valve Solenoid, open circuit. 65 81 Refer to the explanation Pump Motor Relay, open Brake (Stop Lamp) switch under trouble code 41. circuit. Refer to the circuit is shorted or open. 46 explanation under trouble This code indicates a code 41. IMPORTANT - malfunction in the stop Left Front Pulse Width This code may be FALSELY lamp switch circuit. Note Modulation Valve set by an improperly that this code can be set by Solenoid, open circuit. performed trouble code a driver who rides the brake Refer to the explanation clearing procedure. pedal. under trouble code 41. 66 85 47 Pump Motor Relay, short Anti-lock indicator lamp Left Front Isolation Valve circuit. Refer to the circuit is open. This code Solenoid, short circuit. explanation under trouble if present, will be flashed by Refer to the explanation code 41. the brake warning lamp, under trouble code 43. not the anti-lock lamp, and 67 indicates an open circuit in 48 Pump Motor Circuit, open the anti-lock lamp circuit. Left Front Pulse Width circuit. This code indicates 86 Modulation Valve an open circuit in the Solenoid, short circuit. connection between the Anti-lock indicator lamp Refer to the explanation pump motor, and the EHCU circuit is shorted. This under trouble code 43. (Electro-Hydraulic Control code if present, will be Unit). flashed by the brake 51 warning lamp, not the anti- Rear Isolation Valve 68 lock lamp, and indicates a Solenoid, open circuit. Pump Motor Circuit, short circuit in the anti-lock Refer to the explanation shorted circuit. This code lamp circuit. under trouble code 41. indicates a shorted circuit in 88 the connection between the 52 pump motor, and the EHCU Brake warning indicator Rear Pulse Width (Electro-Hydraulic Control lamp circuit is shorted. This code indicates a short circuit in the brake warning 95 indicator lamp circuit. GM Code Scanner Applications & VANS TRUCKS All gasoline burning vehicles 1 ton capacity or less All gasoline burning vehicles 1 ton capacity or less All models All models All models SATURN PONTIAC 6000 6000 STE Bonneville Fiero Firebird Grand Am Grand Prix J2000 LeMans Parisienne Phoenix Safari Safari Wagon Sunbird T1000 Firebird 3.4L, 5.7L Sunbird 2.0L, 3.1L

1994 1995 Achieva Calais Custom Cruiser Cutlass Calais Cutlass Ciera Cutlass Cruiser Cutlass Cruiser Wagon Cutlass Supreme Cutlass Supreme Classic Delta 88 Eighty-Eight Firenza Ninety-Eight Omega Toronado * Touring Sedan Trofeo * 1982-93 OLDSMOBILE 3.4L, 5.7L CHEVROLET Beretta Camaro Caprice Cavalier Celebrity Chevette Citation Corsica Corvette El Camino Impala Lumina Monte Carlo Camaro Cavalier 3.1L Lumina 3.1L Caprice 4.3L Cimarron CADILLAC BUICK Century Electra Electra Wagon Estate Wagon Le Sabre Le Sabre Wagon Park Avenue Reatta * Regal Regal Grand National Riviera * Roadmaster Skyhawk Skylark Somerset Roadmaster 5.7L Code Scanner is only applicable if vehicle DOES NOT HAVE a climate control computer * 96 GM ABS Applications

CARS VANS MAKE YEAR MODEL MAKE YEAR MODEL 1989-90 Electra Chevrolet 1989-93 Astro 1989-90 Park Avenue GM Van 1990-93 G Series Buick 1989-91 Reatta 1989-93 Riviera TRUCKS 1991 Roadmaster MAKE YEAR MODEL 1990-92 Brougham 1988-93 Blazer 1989-90 DeVille Chevrolet 1990-93 Suburban Cadillac 1989-93 Eldorado 1989-90 Fleetwood 1988-94 C Series 1989-93 Seville 1988-94 K Series 1990-91 R Series GM 1989-94 S Series 1991 Caprice Chevrolet 1990-94 T Series 1990-91 Corvette 1990-91 V Series

1989-90 98 Regency 1989-93 Jimmy 1991 Custom Cruiser 1989-93 Safari Oldsmobile 1989-90 Delta 88 1988-93 Sierra 1991-93 Sonoma 1989-92 Toronado GMC 1991-93 Syclone 1990-92 Trofeo 1992-93 Typhoon 1992-93 Yukon Pontiac 1989-90 Bonneville 1989-90 Bonneville SSE Oldsmobile 1991-93 Bravada

Vehicles not listed may be tested for engine/transmission trouble codes only.

97 ONE (1) YEAR LIMITED WARRANTY Bosch warrants to the original purchaser that this product will be free from defects in materials and workmanship for a period of one (1) year from the date of original purchase. Any unit that fails within this period will be replaced or repaired at Bosch’s discretion without charge. If you need to return product, please follow the instructions below. This warranty does not apply to damages (intentional or accidental), alterations or improper or unreasonable use. DISCLAIMER OF WARRANTY BOSCH DISCLAIMS ALL EXPRESS WARRANTIES EXCEPT THOSE THAT APPEAR ABOVE. FURTHER, BOSCH DISCLAIMS ANY IMPLIED WARRANTY OF MERCHANT- ABILITY OF THE GOODS OR FITNESS OF THE GOODS FOR ANY PURPOSE. (TO THE EXTENT ALLOWED BY LAW, ANY IMPLIED WARRANTY OF MERCHANTABILITY OR OF FITNESS APPLICABLE TO ANY PRODUCT IS SUBJECT TO ALL THE TERMS AND CON-DITIONS OF THIS LIMITED WARRANTY. SOME STATES DO NOT ALLOW LIMITATIONS ON HOW LONG AN IMPLIED WARRANTY LASTS, SO THIS LIMITATION MAY NOT APPLY TO A SPECIFIC BUYER.)

LIMITATION OF REMEDIES IN NO CASE SHALL BOSCH BE LIABLE FOR ANY SPECIAL, INCIDENTAL OR CONSE- QUENTIAL DAMAGES BASED UPON ANY LEGAL THEORY INCLUDING, BUT NOT LIM- ITED TO, DAMAGES FOR LOST PROFITS AND/OR INJURY TO PROPERTY. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF INCIDENTAL OR CON- SEQUENTIAL DAMAGES, SO THIS LIMITATION OR EXCLUSION MAY NOT APPLY TO A SPECIFIC BUYER. THIS WARRANTY GIVES YOU SPECIFIC LEGAL RIGHTS, AND YOU MAY ALSO HAVE OTHER RIGHTS WHICH VARY FROM STATE TO STATE.

TO USE YOUR WARRANTY If you need to return the unit, please follow this procedure: 1) Call Bosch Technical Support at 1-(800) 228-7667. Our Technical Service Representatives are trained to assist you. 2) Proof of purchase is required for all warranty claims. For this reason we ask that you retain your sales receipt. 3) In the event that product needs to be returned, the Technical Service Rep- resentative will provide you with the address where you can send the unit. 4) You will need to provide us with a contact name, daytime phone number, and a description of the problem. 5) If possible, return the product in its original package with cables and acces- sories. 6) Include your return address on the outside of the package and send the unit to the address provided by your Technical Service Representative. 7) You will be responsible for shipping charges in the event that your repair is not covered by warranty.

O UT OF WARRANTY REPAIR If you need product repaired after your warranty has expired, please call Technical Support at (800) 228-7667.

All information, illustrations and specifications contained in this manual are based on the latest information available from industry sources at the time of publication. No warranty (expressed or implied) can be made for its accuracy or completeness, nor is any responsibility assumed by Bosch or anyone connected with it for loss or damages suffered through reliance on any information contained in this manual or misuse of accompanying product. Bosch reserves the right to make changes at any time to this manual or accompanying product without obligation to notify any person or organization of such changes.

98