sensor/transmitters may be present. These are the banded type and the stem type. Banded inflation sensors are attached to the wheel’s inner well area via both a peel-off positioning adhesive and a circumferential band clamp. Stem-type sensors mount at the valve 21st CENTURY stem location, with the valve stem an in- tegral part of the sensor. Most OE tire pressure monitoring systems are the stem type, partly to aid in system diagnosis, since the sensor is much more accessible, in terms of dis- tance, by a diagnostic or relearn tool. Band-mounted sensors are located TIRE SERVICE deep inside the wheel, making it more difficult for the signal to pass to the di- BY MIKE MAVRIGIAN agnostic tool, whether the system uses an RF signal or a magnetic signal. Busting tires has served as an auto repair intro Stem-type sensors weigh about an ounce, so this presents no extraordinary for many aspiring techs. Tires have now gone balancing issues. The OE-favored direct type pressure sensors are powered by a 10-year lithi- high-tech, and special tools and techniques are um battery. The expected battery life is realistic, since these sensors are de- required to avoid busting something expensive, signed to operate only during or after a 20-mph speed is reached. When a vehi- even during routine service. cle is parked, the sensors are designed to transmit pressure only once per hour hop owners and technicians ual sensor or monitor mounted inside or so. may have always considered each wheel’s inner well. This system is If a vehicle is equipped with an OE tire and wheel service to be the calibrated to alert the driver when one TPMS and the customer wants a set of low-tech aspect of their work- or more tires have lost at least 20% to aftermarket alloys, pay attention: Not all day. But there’s some new 25% of the programmed or recom- aftermarket wheels will accept the Stechnology out there now that may mended inflation pressure. A receiver stem-type sensor. These sensors require make you reassess that notion. mounted in the vehicle receives individ- a specific valve hole relief design. Most ual wheel sensor signals, then sends this aftermarket wheels, which are designed Tire Pressure information to a central on-board com- to accept only standard snap-in rubber Monitoring Systems puter (ECU), which in turn alerts the valves, do not allow the addition of the A tire pressure monitoring system driver via an in-dash warning signal. stem type transmitter. In this case, you’ll (TPMS) alerts a vehicle’s driver of low- Whenever a low-pressure signal is need to find aftermarket wheels that are er-than-specified tire inflation pressure. processed by the ECU, the in-dash tire designed to accept stem-type sensors. If a vehicle is equipped with run-flat/ze- pressure warning light will illuminate. Instead of incorporating a stem-type ro-pressure tires, a TPMS is absolutely In most cases, if a tire pressure problem direct system, some vehicles rely on in- needed, since most drivers won’t feel is indicated, the warning light will re- formation already monitored by the an- the result of a low-pressure condition main on constantly. However, if the tilock braking system (ABS). This is re- when a run-flat tire loses pressure. warning light blinks, this indicates a sys- ferred to as an indirect TPMS. Since As of 2007, all OEMs will be re- tem fault that must be diagnosed. an insufficiently inflated tire will rotate quired to feature a TPMS on their vehi- If wheel positions are changed on the at a different rate than a properly inflat- cles. This means that the aftermarket vehicle (during the course of tire rota- ed tire, due to the resulting difference service industry must be able to handle tion, for example), individual sensors in rolling tire diameter, the difference in these systems properly and diagnose must be reprogrammed. If the sensors wheel rotation is sensed by the ABS. A system problems. are not reprogrammed, the ECU will signal is then sent to alert the driver via Two types of tire pressure monitoring then assign the pressure data to an in- a warning light. It’s then up to the driver systems are currently in use—direct correct wheel location. to check all four tires to determine and indirect. A direct tire pressure Depending on vehicle make, model which one is underinflated. monitoring system features an individ- and year, one of two direct-type TPM However, if all four tires are equally and Wieck Media Mavrigian Mike photos: Harold A. Perry; Photoillustration: 38 July 2006 July 2006 39 21st CENTURY TIRE SERVICE Photos: Mike Mavrigian Mike Photos: Be careful when dismounting or mounting tires on a wheel This is a typical stem-type tire pressure sensor/transmit- that’s equipped with a TPM sensor. Some OEMs recommend ter installation. It’s essential that the wheel’s inside well removing the retaining nut and dropping the sensor into the area is clean to prevent contamination of the sensor. wheel before attempting bead-breaking or dismounting. underinflated, the ABS might not trig- the lithium sensor’s five-year battery life. ignition key remote control is activated ger the pressure warning, since all The basic receiver display identifies during a pressure sensor reset proce- wheels would rotate at the same speed. each tire by a color-coded light. Each dure. Currently, more than 40 different Indirect TPMSs generally are designed sensor is also color-coded, as is each tire- testing and resetting protocols are in to illuminate the warning light when a valve-mounted washer. The sensors are use. Some aftermarket initializing and single tire’s pressure has dropped by programmed to alert the driver if tire diagnostic tools are make/model/year- about 30% in relation to its official rec- pressure drops to 22 psi. If pressure specific, while others are designed to ommended inflation pressure. drops below that, a red LED on the dis- communicate universally with a broad Aftermarket Systems. The three play illuminates above the individual col- spectrum of OE tire pressure monitor- commonly available aftermarket tire or-coded indicators. As an additional ing systems. pressure monitoring systems are made alert, if air pressure drops to 18 psi, a Sensor Replacement Caution. Be- by Doran, Smar Tire and Schrader. second-level warning activates an audi- fore installing any direct (stem-type) Doran’s PressurePro systems are ble alarm, and the LED will flash red. TPMS sensor, and before mounting a available to suit a wide variety of applica- Schrader’s Generation II Smart Valve tire onto a sensor-equipped wheel, you tions, including passenger vehicles, light- RF TPMS is a direct system comparable must note the sensor’s ID code (printed to heavy-duty trucks, motorhomes, fifth- to OE systems. Individual stem-type on the sensor body). This code will be wheel trailers and tag trailers. The Pres- sensors mounted to each wheel transmit required when programming or repro- surePro installation kits include a dash- data to individual wheel-well-mounted gramming the sensor. Remember to mounted 12-volt monitor and individ- detectors, which in turn send signals to record this number before hiding the ual-wheel sensors that thread onto each the centrally mounted receiver. sensor from view. wheel’s air valve. An audible alarm alerts TPMS Initialization/Diagnostic While specific procedures for initializ- the driver if any tire loses more than Tools. A test tool is required to service ing an indirect TPMS may vary among 12% of its programmed pressure. A sim- any direct TPMS. For aftermarket use, vehicle makes and models, a typical ap- ple programming procedure is outlined easy-to-use hand-held testers are com- proach involves first adjusting each tire’s with the kit’s instructions. monly available. The two most common inflation pressure to the recommended Smar Tire’s system includes four uses for a diagnostic tool are to perform level. With the vehicle stopped, turn the band-mounted wheel-mount pressure a system reset and to test system opera- ignition switch to the ON position. Press sensors and a dash-mounted receiver/ tion. About 75% of the tool’s use will be and hold the tire pressure warning reset display unit. Each pressure sensor for resetting during routine tire or switch (typically located under the dash) weighs a tad under 1.5 oz. These sensors TPMS service. until the tire pressure warning light are said to be accurate to Ϯ1.5 psi. Sen- There is no industry standard regard- blinks three times at 1-second intervals. sor mounting band-straps accommodate ing TPMSs. Some systems require re- Next, operate the vehicle at 19 mph or 13- to 20-in.-diameter wheels. The band setting if primary vehicle battery power more to complete the initialization of is clamped to the wheel’s inner well is interrupted, while this problem is not the skid control ECU. If the tire pres- area. Each sensor features a motion de- an issue in other systems. Depending sure warning light blinks at .25-second tector that powers the sensor down on vehicle make, model and year, some intervals while the vehicle is in motion, when the vehicle is parked, conserving systems’ data may be corrupted if the the initialization may have failed. If this 40 July 2006 21st CENTURY TIRE SERVICE Photo: Mike Mavrigian Mike Photo: SPX/OTC courtesy Photo This hand-held initializing tool is being used to reprogram The diagnostic/relearn tool is placed adjacent to the tire a sensor for wheel location.