On-Board Diagnostics
The ECM has an on board diagnostic system, which detects malfunctions related to engine sensors or actuators. The ECM also records various emission-related diagnostic information. See Fig 1.
The information in Fig 1 can be checked using procedures listed in Fig 2.
The Malfunction Indicator Lamp (MIL) on the instrument panel lights up when the same malfunction is detected in 2 consecutive trips (two trip detection logic), or when the ECM enters fail-safe mode.