For 1990-2009 cars

### Circuit Description

Battery positive voltage is supplied to the malfunction indicator lamp (MIL) through a logic module in the instrument panel cluster (IPC). 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 ignition switch ON and the engine not running.

• | 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 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.

### 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 Connect 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 |

1. Verify whether the instrument cluster is operational.
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 | Inspect the fuse that supplies battery positive voltage to the MIL. Is the fuse open? | -- | Go to Step 10 | Go to Step 4
4 |

1. Turn OFF the ignition.
2. Remove the fuse that supplies voltage to the MIL.
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 5

Go to Step 11

5 |

1. Turn OFF the ignition.
2. Install the fuse that supplies voltage to the MIL.
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 9

Go to Step 6

6 |

1. Turn OFF the ignition.
2. Remove the instrument panel cluster (IPC). Refer to Instrument Cluster Replacement.
3. Probe the MIL battery positive voltage circuit of the IPC harness connector with a test lamp that is connected to a good ground.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 12

7 | 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 15 | Go to Step 8
8 | 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 15 | Go to Step 13
9 | 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 15 | Go to Step 14
10 | Repair the short to ground in the battery positive voltage circuit. Refer to Wiring Repairs. Did you complete the repair? | -- | Go to Step 15 | --
11 | Repair the short to voltage in the MIL control circuit. Refer to Wiring Repairs. Did you complete the repair? | -- | Go to Step 15 | --
12 | Repair the open in the MIL battery positive voltage circuit. Refer to Wiring Repairs. Did you complete the repair? | -- | Go to Step 15 | --
13 | Replace the IPC. Refer to Instrument Cluster Replacement. Did you complete the replacement? | -- | Go to Step 15 | --
14 | Replace the PCM. Refer to Control Module References for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 15 | --
15 |

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 performance, and driveability.
5. Observe the MIL, the vehicle performance, and the drivebility.

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

--

System OK

Go to Diagnostic Trouble Code (DTC) List - Vehicle