Malfunction Indicator Lamp (MIL)

Malfunction Indicator Lamp (MIL)
The Malfunction Indicator Lamp (MIL) looks the same as the MIL you are already familiar with ("CHECK ENGINE" lamp). However, OBD II requires for it illuminate under a strict set of guidelines. Basically, the MIL is turned on when the TCM detects a DTC that will impact the vehicle's emissions.

The MIL is under the control of the Diagnostic Executive. The MIL will be turned on if a component or system which has an impact on vehicle emissions indicates a malfunction or fails to pass an emissions-related diagnostic test. It will stay on until the system or component passes the same test, for three consecutive trips, with no emissions-related faults.