Malfunction Indicator Lamp: Description and Operation

CIRCUIT OPERATION
The service engine soon lamp is used to indicate to the operator a problem in the engine control system. If a problem is detected, the Powertrain Control Module (PCM) sends a message over the CCD Bus to the Body Control Module (BCM).

The BCM interprets this message and sends a signal to the instrument cluster to illuminate the lamp. This lamp also is illuminated, for a few seconds, when the ignition switch is moved from the OFF to the RUN position as a bulb check. The bulb check operation is controlled by the PCM.