For 1990-2009 cars

### Circuit Description

The malfunction indicator lamp (MIL) is illuminated when the ignition is ON and the engine is OFF. Battery ignition voltage is supplied to the MIL. The powertrain control module (PCM) will turn the MIL ON by grounding the lamp control circuit. The MIL is normally off when the engine is running.

### Diagnostic Aids

Check for any of the following conditions:

• | Check for a faulty indicator bulb, or an open in the instrument cluster power circuit if the engine starts and runs OK.

• | Check for a faulty main relay if there is no MIL and the engine cranks but will not start.

• | A MIL that is dim or not illuminated steady can be caused by an inadequate PCM ground. Inspect G102 for a clean, tight connection.

• | A faulty electrical connection to the PCM.

An intermittent malfunction may be caused by a fault in the MIL electrical circuit. Inspect the wiring harness and components for an intermittent condition. Refer to Intermittent Conditions .

### Test Description

The numbers below refer to the step numbers in the diagnostic table.

1. This step checks whether there is communication between the PCM and a scan tool device. If the PCM is unable to provide serial data to the scan tool, there will be no MIL control.

2. If other instrument panel cluster (IPC) functions are not working correctly check for an open GAGE fuse or for a lack of power and ground to the IPC.

3. This step checks for an open MIL Control circuit or for an internal PCM failure.

4. An open fuse determines if a voltage is constantly being applied to the control circuit.

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 |

1. Connect a scan tool.
2. Turn ON the ignition, with the engine OFF.

Does the scan tool display any engine data?

Go to Step 3

Go to Scan Tool Does Not Communicate with Vehicle Control Module/Powertrain Control Module in Data Link Communications

3 | Observe the instrument panel cluster (IPC) assembly operation. Do all other functions of the IPC function normally? | Go to Step 4 | Go to Diagnostic Starting Point - Instrument Panel, Gages and Console in Instrument Panel, Gages, and Console
4 |

1. Turn OFF the ignition.
2. Disconnect PCM electrical connector with the MIL control circuit.
3. Turn ON the ignition, with the engine OFF.
4. Probe the MIL control circuit on the harness side with a 3-amp fuse jumper wire to ground.

Does the MIL illuminate?

Go to Step 9

Go to Step 5

5 | Did the fuse in the jumper wire open? | Go to Step 6 | Go to Step 7
6 | Repair the short to voltage in MIL control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 10 | --
7 |

1. Turn ON the ignition, with the engine OFF.
2. Backprobe the electrical connector C1 terminal 2 of the instrument panel cluster (IPC) assembly with a 3-amp fuse jumper wire to ground.

Does the MIL illuminate?

Go to Step 8

Go to Diagnostic Starting Point - Instrument Panel, Gages and Console in Instrument Panel, Gages, and Console

8 | Repair the open in the MIL control circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Step 10 | --
9 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | Go to Step 10 | --
10 | Turn ON the ignition, with the engine OFF. Is the MIL illuminated? | Go to Step 11 | Go to Step 2
11 |

1. Use the scan tool in order to clear the DTCs.
2. Turn OFF the ignition for 30 seconds.
3. Start the engine.

Observe the MIL operation.

Is the MIL illuminated while the engine is running?

Go to Diagnostic System Check - Engine Controls

System OK