For 1990-2009 cars

### Circuit Description

There should always be a steady malfunction indicator lamp (MIL) when the ignition switch is in the ON position and the engine is not running. System voltage is applied to the indicator bulb. The powertrain control module (PCM) will control the MIL and turn the MIL ON by providing a path to ground.

### Diagnostic Aids

An intermittent malfunction may be caused by a faulty electrical connection in the MIL circuit. Refer to Intermittent Conditions .

### Test Description

The numbers below refer to the step numbers on 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 GAUGE 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, Gauges 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 3 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, Gauges 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.
4. Observe the MIL operation.

Is the MIL illuminated?

Go to Diagnostic System Check - Engine Controls

System OK