Malfunction Indicator Lamp: Testing and Inspection

The malfunction indicator light or check engine light is intended to alert the driver of certain malfunctions in the engine control system. If such a fault occurs, the processor will substitute a value or values and continue operation. This process is called failure effects management (as described previously). In some cases this action may result in a slight change in vehicle driveability.

Check Engine Light Operations
With the system functioning properly, the check engine light will remain on while the key is in the run position. Once the vehicle has been started, the check engine light will go out. With the system not functioning properly, the check engine light may remain on after the vehicle has started. If the light stays on with the engine operating, conduct Key-ON/Engine-OFF self-test to completion. If the light continues to remain on, check other engine/system related components. If the check engine light never comes on check other engine/system related components. If the vehicle does not start, proceed to Pinpoint test A1 (A1 indicates a substep within test A). If the check engine light comes on for a period then goes off, and a service code is present, the code is a continuous code. The check engine light only warns the driver of an input device malfunction. When in self-test, the check engine light will also flash the service codes.