More Toyota Warning Light Precautions

Last month we explained what a blinking light on a Toyota air conditioner button could tell you. In this column, we continue the warning light theme by showing you how much time warning lights can save an alert technician. At the same time, we’ll show you how much aggravation some warning lights can cause a distracted or uninformed technician. There are also cautionary tales here about coping with interrelated systems on modern vehicles. If you don’t know how these sophisticated systems work together, focus on fundamentals first. See if covering the basics – such as tightening a gas cap – solves the vehicle’s problem. As one of my teachers used to say, “Basics beat the baloney any day.” According to Toyota specialists we know, Cautionary Tale Number One is never overlook the brake warning light. The myriad of little graphic symbols in Photo 1 (a Sequoia instrument panel) reminds us of how sophisticated vehicles have become. Sure, this panel has very familiar stuff such as the Check Engine (MIL or Malfunction Indicator Lamp), brake and battery warning lights. But it also has symbols on the left for less-familiar systems such as traction control (TRAC) and vehicle skid control (VSC). Remember that if the brake warning light comes on, systems such as ABS, traction control, skid control and cruise control will fail-safe and their respective warning lights will turn on. As sophisticated as these systems are, they still rely on the safety of a good-working basic brake system. An illuminated brake warning light tells them something fundamental is wrong. Often, all you have to do to turn out the warning lights and put these system back in business is to top off the master cylinder. Naturally, the brake fluid level drops as the brake pads wear. But experience shows that by the time the fluid level in a Toyota master cylinder drops low enough to turn on the warning light, there’s usually plenty of service still left in those brake pads. So, topping off the fluid turns out the brake warning light and turns these related systems on again. There have been instances where uninformed techs ignored the brake warning light and pursued trouble codes in the related systems. Understandably, they were spooked when the VSC computer spit out a scary-sounding communication error code! As long as we’re working around the master cylinder, keep an eye out for a sticking float when refilling or topping off a Toyota master cylinder. Occasionally you have to tap the master cylinder reservoir with a screwdriver handle to dislodge the reservoir float after refilling or topping off. The float works fine after that. Don’t miss the chance to sell a brake fluid change on vehicles that see heavy-duty service or operate in damp, humid climates. The worst thing frequent brake fluid changes do is prolonging the life of expensive hydraulic components! Cautionary Tale Number Two is doesn’t overlook that Check Engine or MIL light. Always fix whatever’s bugging the ECM / PCM first. Then see if this shuts off warning lights such as the VSC and TRAC. Obviously, a Check Engine light turning on indicates a serious emission problem. The root of the emission problem, for example, may be a misfiring engine. MOTOR readers probably know that during extremely slippery road conditions, a traction control computer may tell an ECM to reduce torque. The ECM responds by shutting off injectors to kill some cylinders. However, killing cylinders on an engine that’s already misfiring could create the fatal situation of an engine stalling in the middle of a slippery roadway. Therefore, the traction control shuts itself off until the Check Engine light goes out again.

OVER 8/8/2006 A loose or missing gas cap on a late-model Toyota product has fooled more than one technician. The vehicle happens to be equipped with the traction-control and vehicle skid-control systems. The customer complains that the instrument panel looks like a Christmas tree because the Check Engine, VSC and TRAC warning lights are all illuminated. The tech checking this vehicle has seen hundreds of Check Engine lights on previous vehicles, so seeing another one is old news to him. But he becomes totally distracted by and fascinated with the VSC and TRAC warning lights because he’s never worked on these high-tech systems. Surprise! When the distracted tech retrieves trouble codes from these systems, he gets the dreaded communications error code. Sounds like a big-dollar diagnostic and repair project. Meanwhile, all the vehicle really needs is a properly installed gas cap and a clear-headed technician to erase the evaporative emissions codes! Experience shows that a loose or missing gas cap on a late-model Toyota often leads to a trouble-code hat trick of P0440, P0441 and P0446. Don’t get carried away here because installing or tightening the gas cap usually takes care of all three codes. Cautionary Tale Number Three for this month is check the ECM/PCM for pending codes (sometimes called one-trip codes) before going off on a diagnostic wild-goose chase. For example, a Toyota Avalon comes into your shop with the traction-control and vehicle-skid warning lights illuminated. When you check these systems for codes, you get the dreaded communications error code. What’s wrong? Simple – the gas cap is loose or missing and this Avalon owner has only driven the car long enough to set a pending “evap” emissions code. Therefore, the Check Engine light hasn’t turned on yet. However, the other computers sensed the pending evap code and fail- safed the traction-control and vehicle-skid systems. If the owner had driven the car long enough to complete a second trip, the Check Engine light would have been illuminated along with the TRAC and VSC warning lights. So if your scan tool can read pending codes, check those first before you run yourself in a circle over some interconnected systems that aren’t broken! Finally, remember the convenience of the W terminal when diagnosing a no-Check Engine light condition. The TDCL connector (Photo 2) is located under the left side of the dash on many of the Toyota and Lexus vehicles coming into your shop. Prior to OBD-II, the TDCL contained a W terminal. When you ground W to the E1 terminal with the ignition on/engine off, the Check Engine light should turn on. Obviously, this can be a great time-saver if you’re struggling with the oddball case of a problem vehicle with an apparently inoperative Check Engine light.

8/8/2006