Malfunction Indicator Light (Mil)

MIL will illuminate if a failure occurs with Powertrain Control Module (PCM) or Transmission Control Module (TCM). If a failure occurs associated with TCM, see IMPORTED TRANSMISSION SERVICE & REPAIR section.

When ignition is turned on, MIL should come on. When 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 CODES  .

If MIL lights 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 light. An example of a failure that could occur and not cause MIL to light would be a FUEL LEVEL TOO LOW signal generated on a A4 1.8L model.