Circuit Description
There should always be a steady MIL with the ignition ON, and with the engine OFF. 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 DTC P1671 set suggests an open in the MIL driver circuit.
MIL Operation
The malfunction indicator lamp (MIL) is located on the instrument panel, CHECK ENGINE or SERVICE ENGINE SOON. The MIL performs the following functions:
| • | It 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, with 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. |
Perform the Powertrain On Board Diagnostic (OBD) System Check first, when the following conditions are present:
| • | When the MIL does not turn ON when the ignition switch is turned to the RUN position. |
| • | When 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 |
| • | A broken wire inside the insulation |
Inspect for the following items:
| • | The PCM harness and connectors for: |
| - | Improper mating |
| - | Broken locks |
| - | Improperly formed or damaged terminals |
| - | Poor terminal to wire connection |
| - | Damaged harness |
| • | If the engine runs OK, test for: |
| - | A faulty bulb |
| - | An open in the MIL driver circuit |
| - | An open in the instrument cluster ignition feed |
| • | If the engine cranks but will not run, test for: |
| - | An open PCM ignition or battery feed |
| - | A poor 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 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? | -- | ||
2 | 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 poor 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 programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the action complete? | -- | -- | |
8 | Locate and repair open in PCM battery feed circuit or the PCM ignition feed circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |
9 | Locate and repair short to ground in PCM ignition feed circuit or the PCM battery feed circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- |
