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Check Engine Light Diagnosis and Repair FAQs

Check Engine Light Diagnosis

Helps vehicle owners understand the significance of proper driver response to engine warning lights in a variety of situations
Includes questions related to computer diagnostics and drivability diagnostics issues

Why does my check engine light go on and off?
When a vehicle is being driven, its computer is always checking parameters and sensors to make sure they are all working correctly. If a failure is recognized during this process, the computer can set a fault code and turn on a warning light. If the failure is intermittent, and another check made by the computer no longer finds the failure, the warning light will turn off. When the car is turned off and then restarted, the computer will again check all systems. If the previous problem is not detected, the vehicle passes the computer’s test and the light will remain off.

What does it mean when the check engine light flashes?
A flashing check engine light means the computer is telling the driver that a current failure in the system may be sending too much raw fuel to the catalytic converter. This excess fuel can destroy the converter. In this situation, the recommended procedure is that the driver safely pull off the road, stop the car, and shut the engine off. It is ok to restart the car and resume driving, but if the light begins flashing a second time, the driver should consult the vehicle manual. It will probably recommend having the vehicle towed to a repair shop.

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