Operation CHARM: Car repair manuals for everyone.

Malfunction Indicator Lamp: Testing and Inspection

The check engine lamp should illuminate when the key is ON and the engine is OFF. If it does not turn on, the most likely cause is a faulty bulb. If the bulb is good then test the wiring to the ECM for an open or short to ground. If a complete circuit to the bulb is present then the engine control module is suspect.