Chart A1-1 No Malfunction Indicator Lamp

Diagnostic Chart:

OBD System Circuit:

CIRCUIT DESCRIPTION
There should always be a steady Malfunction Indicator Lamp (MIL) when the ignition is in the "ON" position and the engine is not running. System voltage is applied to the light bulb. The Engine Control Module (ECM) will control the MIL and turn it "ON" by providing a ground path through the PPL/YEL wire.

TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.

1. Checks to see if ECM is receiving power.
2. Checks for an open in the PPL/YEL wire, or for a faulty ECM.
3. Checks for an open in WHT/BLU wire between Main relay and ECM.
4. Checks to see if ECM has a good ground.
5. Checks for an open in BLK/WHT wire to Instrument Panel (I/P) or in PPL/YEL wire to ECM.
6. Checks to see if Main relay switch is receiving power.
7. Checks to see if Main relay coil is receiving power.
8. Checks to see if Main relay or ECM is faulty, or for an open in BLU/BLK wire between Main relay and ECM.

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