Malfunction Indicator Lamp: Description and Operation

Malfunction Indicator Lamp (MIL):

Quad-Driver Module (QDSM) Circuit:

Purpose
The Malfunction Indicator Lamp (MIL), service engine soon, is used to inform the driver of computer related malfunctions. The MIL is also used to interpret trouble codes stored in computer memory. With the MIL it is possible to access computer memory without the use of a scan tool. However, a scan tool is recommended to read diagnostic trouble codes (DLC).

Operation
The MIL should always be illuminated when the ignition is "ON" and the engine is "OFF". Battery voltage is supplied through the ignition switch directly to the lamp. The PCM controls the lamp and turns it "ON", by providing a ground path through CKT 419.

A steady MIL illumination with the engine running suggests a short to ground in the light control CKT 419, or a DTC is set in computer memory.

Location
The MIL is located in the instrument panel cluster.