On-Board Diagnostics: Notes

PCM is equipped with a self-diagnostic system, which detects system failures or abnormalities. When a malfunction occurs, PCM will store a Diagnostic Trouble Code (DTC) and, in most cases, illuminate the Malfunction Indicator Light (MIL) located on instrument cluster. OBD-II requires that PCM illuminate MIL when a malfunction is detected that affects vehicle emissions. Malfunctions are recorded as hard failures or as intermittent failures. If operation of MIL is in question, see MALFUNCTION INDICATOR LIGHT INOPERATIVE  under CIRCUIT TESTS.