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 PCM will turn ON the MIL by grounding the control circuit at the PCM. The MIL is normally OFF when the engine is running. A steady MIL with the engine running suggests a short to ground in the MIL control circuit or a DTC is set in the powertrain control system.

### Diagnostic Aids

Check for any of the following conditions:

• | Check for a shorted MIL control circuit between the PCM and I/P cluster assembly.

• | A shorted I/P cluster assembly board may cause the MIL to stay ON.

• | Check for 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. The Diagnostic System Check-Engine Controls prompts the technician to complete some basic checks and to store the Freeze Frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. This step checks for a short to ground in the MIL control circuit.

3. This step checks for a short in the MIL control circuit between the PCM and the I/P cluster assembly.

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. Turn OFF the ignition.
2. Disconnect the PCM.
3. Turn ON the ignition, leaving the engine OFF.

Did the MIL illuminate?

Go to Step 3

Go to Step 5

3 |

1. Check for a short to ground in the MIL control circuit between the PCM and the I/P cluster assembly.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

Go to Step 6

Go to Step 4

4 |

1. Check the I/P cluster assembly for a shorted circuit board.
2. Replace as necessary.

Is the action complete?

Go to Step 6

--

5 | Important: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | Go to Step 6 | --
6 |

1. Start the engine.
2. Observe the MIL.

Does the MIL turn OFF in approximately 1 to 2 seconds after you start the engine?

System OK

Go to Diagnostic Trouble Code (DTC) List