No Malfunction Indicator Lamp (MIL)

Diagnostic Chart:

Wiring Diagram:

Circuit Description

When the ignition is turned ON, the Malfunction Indicator Lamp (MIL) will momentarily flash ON then OFF and remain ON until the engine is running, if no Diagnostic Trouble Codes (DTC) are stored. Battery voltage is supplied through the ignition switch directly to the MIL telltale. The Powertrain Control Module (PCM) controls the MIL by providing a ground path through the MIL control circuit to turn ON the MIL.

Diagnostic Aids

An open ignition #1 fuse will cause the entire cluster to be inoperative, and may set DTCs P1601 and P1629.

Check the battery and ignition 1 feed circuits for poor connections if the MIL is intermittent.

Any circuitry, that is suspected as causing an intermittent complaint, should be thoroughly checked for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminals to wiring connections or physical damage to wiring harness.

Test Description

Number(s) below refer to step number(s) 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 on the scan tool, if applicable. This creates an electronic copy of the data taken when the malfunction occurred. The information is stored in the scan tool for later reference.

3. Connections that are suspected of being faulty should be thoroughly checked as described in the diagnostic aids.

4. If the engine fails to start and the MIL is inoperative, then the fault can be isolated to either the PCM ignition feed 1, the battery feed, a poor ground at the engine block, or the PCM.

6. Probing the MIL circuit with a test light to ground simulates the PCM's control of the MIL. If the MIL illuminates, then the malfunction can be isolated to the control of the MIL or a poor connection at the MIL terminal to the PCM. Connections that are suspected of being faulty should be thoroughly checked as described in the diagnostic aids.

8. It takes very little resistance for the battery and ignition 1 feed circuits to cause an intermittent condition and should also be checked for a poor connection as described in diagnostics aids.

11. Before replacing the PCM, check for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminals to wiring connections or physical damaged to the wiring harness.

The replacement PCM must be programmed and the crankshaft position system variation procedure must be preformed. Refer to the latest Techline procedure for PCM reprogramming and also refer to the Crankshaft Position System Variation Procedure.

13. A shorted MIL circuit can be diagnosed with a scan tool. Refer to PCM Outputs Diagnosis.

14. An open MIL circuit can be diagnosed with a scan tool. Refer to PCM Outputs Diagnosis.

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

17. For IPC replacement procedures, refer to Instrument Panel Gauges and Warning Indicators.

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

21. PCM grounds will only cause a problem if all of the grounds are not making a good connection. If the PCM ground problem is suspected, the most probable place to check is where all of the grounds meet, at the engine block. Connections that are suspected of being faulty should be thoroughly checked as described in the diagnostic aids.

22. If no faults have been found at this point and no DTCs were set, refer to the diagnostic aids for additional checks and information.