Malfunction Indicator Lamp: Description and Operation

Malfunction Indicator Light (MIL) Location:

Purpose
Fault Detected
The Malfunction Indicator Light (MIL), alerts the driver of a malfunction detected in one or more of the following circuits:
- ECM
- Oxygen sensor
- Air-flow sensor
- Intake air temperature sensor
- Throttle position sensor
- Engine coolant temperature sensor
- Crankshaft Position sensor
- Camshaft Position (TDC) sensor
- Barometric pressure sensor
- Ignition Timing Adjustment Signal
- Injector
- EGR (California only)

Reading Codes
The MIL can also be used to read Fault codes set in memory.

Operation
Bulb Check
- Immediately after the ignition switch is turned ON, the MIL will light for about 5 seconds to verify circuit operation.

Fault Detected
- When the ignition switch is turned off, the light goes out, and will not come back on until the fault re-occurs.
- If a detected problem signal returns to normal the MIL will go out.
- The code will be stored in the ECM memory for 50 start cycles after the last time it was detected.

Reading Codes
See Computers and Control Systems/Testing and Inspection/On Board Diagnostics.