Malfunction Indicator Lamp Circuit Check

Diagnostic Chart:

Circuit Description
When the vehicle's operator initially turns on the ignition, the Malfunction Indicator Lamp (MIL) momentarily flashes on then off and then stays on. When the engine is running and no Diagnostic Trouble Codes (DTCs) are stored, the Vehicle Control Module (VCM) turns off the MIL. The ignition switch supplies battery voltage directly to the MIL telltale. The VCM controls the MIL by providing a ground path through the MIL control circuit in order to turn on the MIL.

Diagnostic Aids
An open gauge fuse will cause the entire IP cluster to be inoperative. Check any circuitry that is suspected of causing an intermittent complaint for the following conditions:

^ Backed out terminals.

^ Improper mating.

^ Broken locks.

^ Improperly formed or damaged terminals.

^ Poor terminal to wiring connections.

^ Physical damage to the wiring harness.

Test Description
The numbers below refer to step numbers on the diagnostic table.

1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data with the scan tool if applicable. This creates an electronic copy of the data when the fault occurred. The information is then stored in the scan tool for later reference.

3. If the engine fails to start and the MIL is inoperative, then the fault can be isolated to either the VCM ignition feed (ECM-1 fuse), the battery feed (ECM-BATT fuse), a poor VCM ground at the engine block, or the VCM.

4. A MIL that responds correctly to the scan tool commands indicates that the fault is not present at this time or that the condition that caused the No MIL condition has been corrected.

5. This step isolates a VCM problem from a circuit problem.

6. Locate and repair any shorts that may have caused the fuse to open before replacing the fuse.

7. This step checks the MIL control circuit for a short to voltage.

16. For MIL bulb replacement procedures, refer to Instrument Panel, Gauges and Warning Lamps.

17. For IP replacement procedures, refer to Instrument Panel, Gauges and Warning Lamps.

19. VCM grounds will only cause a problem if all of the grounds are not making a good connection. If a VCM ground problem is suspected, the most probable place to check is where all the grounds meet at the engine block.