Malfunction Indicator Lamp: Description and Operation

As a functional test, the Malfunction Indicator Lamp (MIL) illuminates at key-on before engine cranking. Whenever the Powertrain Control Module (PCM) sets a diagnostic trouble code that effects vehicle emissions, it illuminates the MIL. The PCM illuminates the MIL only for diagnostic trouble codes that effect vehicle emissions. The MIL remains on until the diagnostic trouble code is erased. The MIL either flashes or illuminates continuously when the PCM detects active engine misfire.

During active misfire, the PCM records the current engine operating conditions. The engine operating conditions are recorded by the PCM.