Refer to Engine Control Schematics
Power, Ground, MIL and Data Link
for
a wiring diagram.
Circuit Description
There should always be a steady malfunction indicator lamp (MIL) with the ignition ON, and with the engine OFF. The ignition feed voltage is supplied directly to the MIL bulb. The Powertrain Control Module (PCM) turns ON the MIL by grounding the MIL driver circuit. No MIL with the ignition ON, with the engine OFF, and with DTC P1671 set suggests an open in the MIL driver circuit.
MIL Operation
The MIL is located on the instrument panel CHECK ENGINE display or on the SERVICE ENGINE SOON display. The MIL performs the following functions:
| • | Informs the driver that a problem has occurred, and that the vehicle should be taken for service as soon as possible. |
| • | As a bulb test and system test, the MIL will illuminate with the ignition ON, and the engine OFF. 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 as long as the ignition is ON. |
| • | If the MIL is not illuminated, and the engine stalls, the MIL will not illuminate until the ignition is cycled OFF, then ON. |
When the following conditions are present, perform the Powertrain On Board Diagnostic (OBD) System Check first:
| • | 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 the following conditions: |
| - | Poor connections |
| - | Rubbed through wire insulation |
| - | Broken wire inside the insulation |
| - | Damaged harness |
| - | Improper mating |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wire connection |
| • | Inspect all wiring and connections of the PCM harness. |
| • | If the engine cranks but will not run, test for an open PCM ignition, for a faulty battery feed, or a faulty PCM to engine ground. |
Test Description
The numbers below refer to the step numbers on the diagnostic table:
-
If the MIL DTC is set, the MIL Control Circuit table will better diagnose the condition.
-
Using a test lamp connected to B+, probe each of the PCM ground terminals in order to ensure that a good ground is present.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Did you perform the Powertrain On Board Diagnostic (OBD) System Check? | -- | ||
Is DTC P0650 set? | -- | Go to DTC P0650 Malfunction Indicator Lamp (MIL) Control Circuit | ||
3 | Inspect the PCM feed fuses. Are the fuses open? | -- | ||
4 |
Does the test lamp illuminate? | -- | ||
5 | Probe the PCM battery feed circuit, using a test lamp that is connected to a good ground. Does the test lamp illuminate? | -- | ||
Inspect for faulty PCM grounds or for faulty PCM ground connections. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems. Did you find and correct the condition? | -- | |||
7 |
Important: The replacement PCM must be reprogrammed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Did you complete the replacement? | -- | -- | |
8 | Locate and repair the open in the PCM battery feed circuit, or in the PCM ignition feed circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- | |
9 | Locate and repair the short to ground in the PCM ignition feed circuit, or in the PCM battery feed circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | -- |
