Malfunction Indicator Lamp (MIL)

The Malfunction Indicator Lamp (MIL) is required by On-Board Diagnostics (OBD II) to illuminate under a strict set of guidelines.

Basically, the MIL is turned ON when the Engine Control Module (ECM) detects a DTC that will impact the vehicle emissions.

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