Circuit Description
There should be a steady malfunction indicator lamp (MIL) with the ignition ON and the engine not running. Ignition feed voltage is supplied directly to the MIL bulb. The powertrain control module (PCM) turns the MIL ON by grounding the MIL control circuit.
MIL Operation
The MIL is located on the instrument panel (CHECK ENGINE) or (SERVICE ENGINE SOON). The MIL performs the following functions:
| • | Informs the driver that a problem has occurred and that the vehicle should be serviced as soon as possible. |
| • | As a bulb check and system check, the MIL will illuminate with the ignition and the engine not running. When the engine is started, the MIL will turn OFF. If the MIL remains ON, the self-diagnostic system has detected a problem. If the problem goes away, the MIL will turn OFF in most cases, but a diagnostic trouble code will remain stored. |
| • | If the MIL is illuminated, then the engine stalls, the MIL will remain Illuminated so long as the ignition switch is ON. |
| • | If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON. |
Perform the Powertrain On Board Diagnostic (OBD) System Check first, when the following conditions are present:
| • | The MIL does not turn ON when the ignition switch is turned to the RUN position. |
| • | The MIL remains ON while the engine is running. |
| • | When you suspect a driveability problem. |
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check the following items:
| • | Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. |
| • | If the engine runs OK, check for a malfunctioning light bulb, an open in the MIL control circuit, or an open in the instrument cluster ignition feed. |
| • | If the engine cranks but will not run, check for an open PCM ignition or battery feed or a poor PCM to engine ground. |
Test Description
The numbers below refer to the step numbers on the diagnostic table.
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A no MIL condition accompanied by a no start condition suggests a faulty PCM ignition feed or battery feed circuit.
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Using a test lamp connected to B+, probe each of the PCM ground terminals to ensure that a good ground is present.
Step | Action | Values | Yes | No |
1 | Was the Powertrain On Board Diagnostic (OBD) System Check performed? | -- | ||
2 | Is DTC P0650 stored? | -- | Go to DTC P0650 Malfunction Indicator Lamp (MIL) Control Circuit | |
3 | Check the PCM ignition feeds and battery feed fuses. Are the fuses OK? | -- | ||
Does the test lamp illuminate? | -- | |||
5 | Use a test lamp connected to ground in order to probe the battery feed circuit at the PCM harness connector. Does the test lamp illuminate? | -- | ||
6 |
Was a problem found? | -- | ||
Locate and repair an open in PCM battery feed circuit or PCM ignition feed circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | ||
8 |
Important:: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | |
9 | Locate and repair a short to ground in the PCM ignition feed circuit or PCM battery feed circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- |
