What to do when the check engine light comes on

If your "check engine" light illuminates don't react like one Connecticut motorist, who simply poured an extra quart of engine oil into her 2002 Toyota Corolla. Although extreme situations, such as low oil pressure or an overheating engine, might trigger a "check engine" light, your dashboard has other lights and gauges to warn you about those problems and probably a lot sooner. The best advice is to read your owner's manual beforehand and learn the purpose of the "check engine" light and every other gauge and warning indicator on your dashboard. Periodically, you also should test the "check engine" light and other dashboard warning lights. Usually, you can do this by turning the key to the key-on/engine-off position. Consult the owner's manual for more information. Replace any bulbs that aren't working.

If the "check engine" light illuminates, it will either blink or remain constant, depending on the problem. Either way, you should have the vehicle checked by a mechanic, although a blinking light or, on some cars, a red light instead of a yellow/orange light indicates a problem that needs immediate attention. In late-model cars, a blinking light usually indicates an engine misfire so severe that unburned fuel is being dumped into the exhaust system, where it can quickly damage the catalytic converter, requiring an expensive repair. If that happens, you should reduce power and have the car or truck looked at as soon as possible. If the light is steady, the problem is not an emergency, but you should schedule an appointment as soon as possible. Today's automotive computers often try to compensate when there's a problem; so you may not notice deterioration in performance, even though your fuel mileage is suffering and your vehicle is emitting unacceptable levels of hydrocarbons and other pollutants.

"The customer is really, in the long run, potentially hurting their pocket book by leaving that light on and ignoring it," says Jim Collins, a national training team leader for Ford Motor Company. In some extreme cases, the car's computer may reduce power for you, as it tries to limit the risk of damage.

If the check-engine light comes on, here are some tips on what you should do:

• Look for a serious problem that requires immediate attention. Check your dashboard gauges and lights for indications of low oil pressure or overheating. These conditions mean you should pull over and shut off the engine as soon as you can find a safe place to do so. On some cars, a yellow "check engine" means investigate the problem, while a red "check engine" means stop right now.
• Try tightening your gas cap. This often solves the problem. Keep in mind that it may take several trips before the light resets. Some vehicles have a separate indicator that warns of a loose gas cap before the condition sets off the "check engine" light.
• Reduce speed and load. If the "check engine" light is blinking or you notice any serious performance problems, such as a loss of power, reduce your speed and try to reduce the load on the engine. For example, it would be a good idea to stop towing a trailer. Have the car checked as soon as possible to prevent expensive damage.
• Contact OnStar, if available. If you have a 1997 or later General Motors vehicle equipped with OnStar and an active OnStar subscription, contact an advisor who can read the trouble code remotely and advise you about what to do.
• Have the code read and the problem fixed. If you want to diagnose the malfunction yourself, you can buy a scan tool at most auto parts stores. Prices range from about $40 to several hundred, depending on the model and the features. The tools come with instructions on how to hook them up and decipher the codes. But unless you have a good knowledge of automotive diagnostics, you're probably better off taking the vehicle to a professional. Some automotive parts stores will read and interpret the code for you without charge. Unless there is an easy fix, they may simply refer you to a mechanic.
• Don't go for a state emissions test. In a late-model car, an illuminated "check engine" light probably is a sure sign your car will fail the test. In some states, it's an automatic failure, even if the problem was nothing more than a loose gas cap. By the way, don't bother trying to fool the inspection station by disconnecting the battery or using any other method to erase the trouble code and turn off the "check engine" light. Your vehicle's computer will let the inspection station know that its codes have been erased, and you'll just have to go back again.

**Courtesy of Consumer Reports