Malfunction Indicator Lamp (MIL): Notes

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.