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 (DTCs) 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 inoperatve, 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
The number(s) below refer(s) to the step number(s) on the Diagnostic Table.
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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.
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Connections that are suspected of being faulty should be thoroughly checked as described in the diagnostic aids.
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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.
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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 malfunctioning should be thoroughly checked as described in the diagnostic aids.
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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 connection as described in diagnostic aids.
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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.
Reprogram the replacement PCM and perform the crankshaft position system variation learning procedure. Refer to the latest Techline information for PCM programming and Powertrain Control Module (PCM) for the Crankshaft Position System Variation Learning Procedure.
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A shorted MIL circuit can be diagnosed with a scan tool. Refer to Powertrain Control Module Outputs Diagnosis .
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An open MIL circuit can be diagnosed with a scan tool. Refer to Powertrain Control Module Outputs Diagnosis .
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For MIL bulb replacement procedures, refer to Instrument Panel and Console of the service manual.
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For IPC replacement procedures, refer to Instrument Panel and Console of the service manual.
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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 of the grounds meet, at the engine block.
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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.
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If no faults are present at this point and no DTCs were set, refer to the diagnostic aids for additional checks and information.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to | ||
2 | Turn ON the ignition switch leaving the engine OFF. Is the MIL ON? | -- | ||
Check for a poor connection in the battery feed or ignition 1 circuits and repair the circuits as necessary. Was a repair necessary? | -- | |||
Attempt to start the engine. Does engine start? | -- | |||
5 | Check for a malfunctioning PCM ground connection at the engine block or PCM connector ground terminals and repair the connection as necessary. Is the action complete? | -- | -- | |
Is the MIL ON? | -- | |||
7 | Inspect the ignition and battery feed fuses. Are the fuses OK? | -- | ||
Check for a poor connection in the battery feed, ignition 1, or the MIL control circuits and repair the connection as necessary. Was a repair necessary? | -- | |||
9 | Did the test light illuminate? | -- | ||
10 |
Does the test light illuminate? | -- | ||
Is the action complete? | -- | -- | ||
12 | Replace the PCM. Is the action complete? | -- | -- | |
Repair the short to voltage in the MIL control circuit. Is the action complete? | -- | -- | ||
Check for an open or a poor connection in the MIL control circuit and repair circuit as necessary. Was a repair necessary? | -- | |||
15 | With a test light still connected to the ground, probe the ignition feed 1 terminal. Does the test light illuminate? | -- | ||
16 | Repair open battery feed circuit. Is the action complete? | -- | -- | |
17 | Check for an open ignition feed circuit or fuse to the MIL and repair as necessary. Was a repair necessary? | -- | ||
18 | Check for a poor connection in the battery feed or the ignition 1 circuits and repair the connection as necessary. Was a repair necessary? | -- | ||
19 | Repair the open in the ignition feed 1 circuit. Is the action complete? | -- | -- | |
Replace the IPC. Refer to Instrument Panel and Console of the service manual. Is the action complete? | -- | -- | ||
Check for a malfunctioning PCM ground connection at the engine block or the PCM connector and repair the connection as necessary. Was a repair necessary? | -- | |||
Does the scan tool display any DTCs that you have not diagnosed? | -- | Go to the applicable DTC table | System OK, refer to Diagnostic Aids. |
