Let's Talk Cars: Check Engine Light

Many drivers are not really clear on what an illuminated "check engine" or "service engine soon" light is telling them, since its meaning is not as straightforward as the "oil pressure" or "temperature" light. An owner's manual provides the best explanation of each warning light in your vehicle. Understanding these indicators and knowing what action to take allows you to nip a problem in the bud and prevent major damage.

In general, if the "check engine" or "service engine soon" light is illuminated, it indicates that the vehicle's computer has detected a malfunction of an engine, fuel, or emissions component, or a system failure. Problems that may trigger the light include:

A failed sensor, such as oxygen, coolant temperature, MAP (manifold absolute pressure), or airflow meters.
Engine problems, such as poor performance, faulty spark plugs and wires, or clogged fuel injectors.
Emissions problems, such as loose or cracked vacuum hose, loose or missing gas cap, or a failed EGR (exhaust gas recirculation) valve.
Electrical wiring that has a short or open circuit.

How you should react to the light depends on how the light behaves. If the light comes on for a little while and then goes out, you may have a momentary problem in the system. Once the light goes out, the problem is no longer occurring, but it may have caused the computer to store a diagnostic trouble code in its memory. Take the car to your repair shop when you have a chance and explain the problem.

If the light comes on and stays on, it indicates an ongoing problem. While the problem may not be severe, it may affect your car's performance, gas mileage, and emission levels. Take it to a repair shop as soon as possible.

If the light flashes on and off, the car has a severe problem that will cause additional damage. If your repair shop is nearby, take the car in right away. If not, shut off the car and call for assistance. It is important to have a repair technician investigate and determine the cause of a flashing "check engine" or "service engine soon" light. If the light is ignored, damage to important components may result.

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Published in the January/February 2002 issue of the AAA Traveler.