Malfunction Indicator Light: Notes

When ignition is turned on, Malfunction Indicator Light (MIL) should illuminate. After engine is started, MIL should turn off after a couple of seconds. If MIL does not turn off after engine is started, or if MIL comes on while driving, retrieve Diagnostic Trouble Codes (DTCs). See RETRIEVING DIAGNOSTIC TROUBLE CODES .

MIL illuminates if a failure is recognized by Engine Control Module (ECM), Anti-Lock Brake System (ABS) control module or Transmission Control Module (TCM). If a failure occurs associated with TCM, see appropriate DIAGNOSTICS article in TRANSMISSIONS. If a failure occurs associated with TCM, see appropriate DIAGNOSTICS article in TRANSMISSIONS. If a failure occurs associated with ABS, see appropriate ANTI-LOCK article in BRAKES.

If MIL illuminates continuously, a malfunction is present that will cause an increase in emissions. If MIL starts to blink, a malfunction is present which may lead to catalytic converter damage. Repair these failures as quickly as possible. For some failures, MIL is only turned on after failure occurs after 2 successive trips with cold engine starts preceding failure.

Some failures will set a DTC which will never cause MIL to illuminate. An example of a failure that could occur and not cause MIL to illuminate would be a FUEL LEVEL TOO LOW signal generated on a A4 1.8L model.

If MIL is on continuously and no DTCs are stored, or if MIL never illuminates, perform MIL check. See MALFUNCTION INDICATOR LIGHT CHECK .