For 1990-2009 cars

Refer to

#### PCM Data Link Connector (DLC) and Malfunction Indicator Lamp (MIL)

and

#### PCM Power and Ground

.

### Circuit Description

The malfunction indicator lamp (MIL) is illuminated if 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. The MIL should be OFF if 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 a shorted MIL control circuit between the PCM, I/P Cluster Assembly, and the duty check data link connector.

• | A shorted IPC assembly board may cause the MIL to stay ON.

• | A faulty electrical connection to the PCM.

An intermittent malfunction may be caused by a problem in the MIL electrical circuit. 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 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 MIL control circuit.

3. This step checks for a short in the MIL control circuit between the PCM and the duty check data link connector 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 ON?

--

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.

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. Repair or replace as necessary.

Is the action complete?

--

Go to Step 6

--

5 | 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