Malfunction Indicator Lamp: Description and Operation

MALFUNCTION INDICATOR LAMP (MIL)

CHECK ENGINE, SERVICE ENGINE SOON, Or ISO Standard Engine Symbol:

The MIL notifies the driver that the powertrain control module (PCM) has detected an on board diagnostic (OBD) emission-related component or system concern. When this occurs, an OBD diagnostic trouble code (DTC) sets.
- The MIL is located in the instrument cluster and is labeled CHECK ENGINE, SERVICE ENGINE SOON or the international standards organization (ISO) standard engine symbol.
- The MIL is illuminated during the instrument cluster prove out for approximately 4 seconds.
- The MIL remains illuminated after instrument cluster prove out if:
- an emission-related concern and DTC exists.
- the PCM does not send a control message to the instrument cluster (applications with the MIL controlled through the communication link).
- the PCM is operating in the hardware limited operation strategy (HLOS).

- The MIL remains off during the instrument cluster prove out if an indicator or instrument cluster concern is present.
- To turn off the MIL after a repair, a reset command from the scan tool must be sent, or 3 consecutive drive cycles must be completed without a concern.
- For all MIL concerns, go to Symptom Charts. Symptom Related Diagnostic Procedures
- If the MIL flashes at a steady rate, a severe misfire condition may exist.
- If the MIL flashes erratically, the PCM can reset while cranking if the battery voltage is low.
- The MIL flashes after a period of time with the key in the RUN position (engine not running) if DTC P1000 is set.