Malfunction Indicator Lamp: Description and Operation

The "CHECK ENGINE" light (also referred to as Malfunction Indicator Light, MIL), is located on the lower left side of the instrument cluster below the temperature gauge. It is intended to alert the driver of certain malfunctions in the EEC system. If the light is "ON," service should be sought as soon as possible.

NOTE: It is not necessary to stop driving and have the vehicle towed if the "CHECK ENGINE" light comes on.

As a bulb check, the "CHECK ENGINE" light illuminates when the ignition is first turned "ON." The ECA computer turns the light out as soon as it receives the PIP (cranking) signal.

The "CHECK ENGINE" light will come on while the engine is operating in Failure Mode Effects Management (FMEM) or Hardware Limited Operation Strategy (HLOS) modes. The light will stay on as long as any faults causing it are present.

In FMEM mode, the ECA computer is receiving one or more sensor signals outside set calibration limits. The computer processor will substitute fixed in-limit sensor values and continue to monitor the faulty inputs. If operation resumes within limits, the ECA will return to normal operation and the "CHECK ENGINE" light will go out. When FMEM is in effect, Engine Running Service Code 98 will be displayed.

HLOS mode is used when the system fault(s) is too extreme for FMEM mode to handle. In HLOS mode, all software operations have stopped and the ECA computer processor is running on hardware control only. The default mode has a minimal calibration strictly to allow the vehicle to operate until service is obtained. Self-Test codes will not be output in HLOS mode.

Faults with the following inputs can activate the "CHECK ENGINE" light:

^ Engine coolant temperature
^ Air charge temperature
^ Barometric pressure
^ Mass air flow
^ Exhaust gas oxygen sensor
^ Throttle position
^ Ignition diagnostic monitor
^ Idle speed control