For 1990-2009 cars

Refer to

#### Cell 21: MIL and DLC

and

#### Cell 21: Power and Ground

.

### Circuit Description

The malfunction indicator lamp (MIL) illuminates when the ignition is ON, and the engine is OFF. Battery ignition voltage is supplied to the MIL. The PCM will turn the MIL ON by grounding the control circuit at the PCM. Under normal conditions, the MIL is 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 the instrument panel cluster assembly.

• | A shorted board in the instrument panel cluster assembly may cause the MIL to stay ON.

• | Check for a faulty electrical connection to the PCM.

A fault in the MIL electrical circuit may cause an intermittent malfunction. Inspect the wiring harness and the components for any of the following conditions:

• | Backed out terminals.

• | Incorrect mating of terminals.

• | Broken electrical connector locks.

• | Incorrectly formed terminals or damaged terminals.

• | Faulty terminal-to-wire connections.

• | Physical damage to the wiring harness.

• | A broken wire inside the insulation.

• | Corrosion of electrical connections, of splices, or of terminals.

### Test Description

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

1. The Powertrain OBD System Check prompts the technician to complete some basic checks, and to save the applicable freeze frame data on the scan tool. This creates an electronic copy of the data that was taken when the fault occurred. The scan tool saves the information 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 | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | Go to Step 2 | Go to Powertrain On Board Diagnostic (OBD) System Check
2 |

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

Is the MIL illuminated?

--

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 IP cluster assembly connector.
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 instrument panel cluster assembly for a shorted circuit board.
2. Repair or replace the instrument panel cluster assembly as necessary. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges, and Console.

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 | Start the engine, and observe the MIL. Does the MIL turn OFF in approximately 1 to 2 seconds after the engine is started? | -- | System OK | Go to the applicable diagnostic table