For 1990-2009 cars

### Circuit Description

The malfunction indicator lamp (MIL) is located on the instrument panel cluster (IPC).

Ignition voltage is supplied to the MIL. The powertrain control module (PCM) turns the MIL ON by grounding the MIL control circuit. There should be a steady MIL with the ignition ON and the engine OFF.

#### MIL Function

• | The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible.

• | The MIL illuminates during a bulb test and a system test.

• | A DTC will be stored if a MIL is requested by the PCM.

#### MIL Illumination

• | The MIL will illuminate with the ignition switch ON and the engine OFF.

• | The MIL will turn OFF when the engine is started.

• | The MIL will remain ON if the self-diagnostic system has detected a malfunction.

• | The MIL may turn OFF if the malfunction is not present.

• | If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated as 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.

### Test Description

The number below refers to the step number on the diagnostic table.

1. This step tests for a short to voltage on the MIL control circuit. With the fuse removed there should be no voltage on the MIL control circuit.

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
Schematic Reference: Engine Controls Schematics Connector End View Reference: Powertrain Control Module Connector End Views or Engine Controls Connector End Views
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle
2 | Command the malfunction indicator lamp (MIL) ON and OFF with a scan tool. Does the MIL turn ON and OFF when commanded with a scan tool? | -- | Go to Intermittent Conditions | Go to Step 3
3 |

1. Turn OFF the ignition.
2. Remove the fuse that supplies voltage to the instrument panel cluster (IPC).
3. Disconnect the powertrain control module (PCM).
4. Turn ON the ignition, with the engine OFF.
5. Measure the voltage from the MIL control circuit in the PCM harness connector to a good ground.

Is the voltage less than the specified value?

0.3 V

Go to Step 4

Go to Step 8

4 |

1. Turn OFF the ignition.
2. Install the fuse that supplies voltage to the IPC.
3. Turn ON the ignition with the engine OFF.
4. Connect a 3-amp fused jumper wire between the MIL control circuit in the PCM harness connector and a good ground.

Is the MIL illuminated?

--

Go to Step 7

Go to Step 5

5 | Test the MIL control circuit for an open or high resistance. Refer to Circuit Testing and Wiring Repairs . Did you find and correct a condition? | -- | Go to Step 11 | Go to Step 6
6 | Test for an intermittent and for a poor connection at the IPC. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs . Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9
7 | Test for an intermittent and for a poor connection at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10
8 | Repair the short to voltage in the MIL control circuit. Refer to Wiring Repairs . Did you complete the repair? | -- | Go to Step 11 | --
9 | Replace the IPC. Refer to Instrument Cluster Replacement . Did you complete the replacement? | -- | Go to Step 11 | --
10 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 11 | --
11 |

1. Remove all test equipment.
2. Connect any disconnected components or any disconnected fuses.
3. Turn OFF the ignition for 30 seconds.
4. Start the engine and operate the vehicle to verify the performance, and driveability.
5. Observe the MIL, the vehicle performance, and the driveability.

Does the vehicle operate correctly, without MIL illumination and without stored DTCs?

--

System OK

Go to Diagnostic Trouble Code (DTC) List - Vehicle