"Check Engine" or "Service Engine Soon" Lamp (CEL)

Purpose:
The malfunction indicator lamp (MIL) (previously called "SERVICE ENGINE SOON") is used by the PCM to signal the operator of the vehicle of a possible problem.

Operation:
When the PCM requires the indicator lamp to be turned on, it will supply a ground signal for the lamp. If the microprocessor is disabled for any reason, a ground for the check engine indicator lamp will be automatically provided.