Malfunction Indicator Lamp: Description and Operation

PURPOSE
The Malfunction Indicator Lamp (MIL), "Service Engine Soon" light has the following purposes:
- Inform the driver that a problem has occurred, and that the vehicle should be taken for service as soon as reasonably possible.
- Displays Diagnostic Trouble Codes (DTC) stored by the ECM helping the technician diagnose system faults.
- Indicates "Open Loop" or "Closed Loop" operation.

OPERATION
The MIL will come "ON" with the key "ON" and the engine not running. When the engine is started, the light will turn "OFF.". This is a bulb and system check. If the light remains "ON," the self-diagnostic system has detected a problem. If the problem goes away, the light will go out in most cases after 10 seconds, but a DTC will remain stored in the ECM.