What to do when your Check Engine Light comes on

If your 'Check Engine' light comes on, first check the gas cap to make sure it wasn't left loose after a recent refueling -- sometimes this can trigger the 'Check Engine' light. Remove the gas cap, and then tighten it firmly again. If the cap was loose, the light should go out after a few short trips.

If the gas cap wasn't the problem and the light continues to steadily glow, have the system checked out as soon as possible. It may not be a major problem though it may affect your car's performance, gas mileage, and emission levels. Isolated or one-time fault signals are usually wiped from the car's engine management system's memory within a few driving cycles, but persistent or serious faults are stored and can continue to trigger the warning light. A light that flashes requires more prompt attention, indicating a more severe condition that must be checked out immediately to prevent damage to the catalytic converter. When you experience a flashing light, minimize driving at high speeds or under heavy loads.


When scheduling service, make sure the automotive shop that diagnoses your car has professional technicians who are properly trained and certified for OBDII diagnosis and repair. The technician will connect your vehicle's computer to a diagnostic computer, which will provide a "trouble" code to assist the technician in determiming why the 'Check Engine' light was activated.

The oxygen sensor is among the most common causes of a "check engine" warning. A degraded oxygen sensor can increase fuel consumption by 10 to 15 percent. However, it can be a gradual deterioration of the sensor and the driver may not notice the resulting reduction in overall engine performance.

Other problems may trigger the engine warning light to come on as well. They include:

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

While the diagnostic computer is connected to your car, the technician can check the idle speed, throttle response, engine temperature, fuel system pressure, manifold vacuum, exhaust emission levels, and many other key indicators. Once the problem is diagnosed and fixed, your car's computer makes sure everything is back to normal, and then turns off the 'Check Engine' light.

The Car Care Council recommends reading your vehicle owner's manual and familiarizing yourself with the purpose of the 'Check Engine' light and every other gauge and warning indicator on your dashboard. The Car Care Council is AskPatty's source of information for the "Be Car Care Aware" consumer education campaign promoting the benefits of regular vehicle care, maintenance and repair to consumers. For more information, visit www.carcare.org.

Take it from us, you don't want to ignore this light. Most repair shops will charge a minor fee for a diagnosis, but waiting to have it checked can lead to expensive and costly repairs down the road, as one of our own editors learned, first-hand.