Malfunction Indicator Lamp: Description and Operation

"Check Engine" Or "Service Engine Soon" Lamp (CEL)
This warning lamp, located on the instrument panel, serves two purposes: to alert the vehicle operator that a fault has been detected in the system and should be serviced as soon as possible and as a diagnostic aid to display trouble codes. The "Check Engine" Lamp (CEL) and "Service Engine Soon" lamp perform the same function and which light is used depends on particular vehicle application.

This lamp will illuminate with the ignition key on and the engine not running. When the engine is started, the lamp should go out. If the lamp remains lit, the self-diagnostic system has detected a malfunction. If the malfunction clears, the lamp will go out after ten seconds and a trouble code will be stored in the ECM.