Malfunction Indicator Lamp: Description and Operation

The check engine lamp on the instrument panel will illuminate if the SMEC or SBEC receives an incorrect signal or no signal from the coolant temperature sensor, charge temperature sensor, MAP sensor, throttle position sensor, battery voltage sensor input or a emission related system (Calif. models) depending on vehicle application. This lamp indicates that the SMEC or SBEC has gone into the "limp in mode" to keep the system operational, and indicates an immediate need for service.
The check engine lamp will also light for several seconds each time the ignition key is turned on as a bulb check.