Malfunction Indicator Lamp (MIL) Inoperative

Circuit Description

When the ignition is turned ON, the MIL will momentarily flash ON then OFF and remain ON until the engine is running, if no Diagnostic Trouble Codes (DTC) are stored. 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 P1629 and U1016.

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

The number(s) below refer(s) to the step number(s) on the Diagnostic Table.

1. The Powertrain OBD System Check prompts you to complete some of the basic checks and to store the freeze frame and failure records data on the scan tool, if applicable. This creates an electronic copy of the data captured when the malfunction occurred. The scan tool stores this data for later reference.

3. Connections that are suspected of being malfunctioning should be thoroughly checked as described in the Diagnostic Aids.

4. If the engine fails to start and the MIL is inoperative, then the malfunction can be isolated to one of the following items:

^ Open PCM ignition feed 1 circuit

^ Open battery feed circuit

^ Poor ground at the engine block

^ Malfunctioning PCM

6. Probing the MIL circuit with a test light to ground simulates the PCMs control of the MIL. If the MIL illuminates, then the malfunction can be isolated to the control of the MIL or a poor electrical connection at the MIL terminal to the PCM. Electrical connections that are suspected of malfunctioning should be thoroughly checked as described in the Diagnostic Aids.

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

12. Reprogram the replacement PCM and perform the crankshaft position system variation learn procedure. Refer to the latest Techline information for PCM programming and CKP System Variation Learn Procedure.

Before replacing the PCM, check for the following condition(s):

^ Backed out terminals

^ Improper mating

^ Broken locks

^ Improperly formed or damaged terminals

^ Poor terminals to wiring connections

^ Physical damaged to the wiring harness

13. A shorted MIL circuit can be diagnosed with a scan tool. Refer to PCM Outputs Diagnosis 2.4L or PCM Outputs Diagnosis 2.2L. Component Tests and General Diagnostics

14. An open MIL circuit can be diagnosed with a scan tool. Refer to PCM Outputs Diagnosis 2.4L or PCM Outputs Diagnosis 2.2L.

20. For Instrument Panel Cluster (IPC) replacement procedures, refer to IP Cluster Replacement (Chevrolet) or IP Cluster Replacement (Pontiac) in Instrument Panel, Gauges and Console.

21. The 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 malfunctioning should be thoroughly checked as described in the Diagnostic Aids.

22. If no malfunctions are present at this point and no DTCs were set, refer to the Diagnostic Aids for additional checks and information.