Diagnostic Aids

If engine starts and runs okay and MIL will not illuminate, check for a faulty indicator bulb or an open in instrument cluster power circuit. If engine cranks but will not start and MIL will not illuminate, check for a faulty main relay. If MIL is dim or does not illuminate steadily, check for a poor PCM ground. Check for a poor connection to PCM.

An intermittent malfunction may be caused by a poor connection, rubbed-through wire insulation, or a wire broken inside insulation. Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, or poor terminal-to-wire connections before component replacement.