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 illuminates if the ignition is ON, and the engine is OFF. Battery ignition voltage is supplied to the MIL. The powertrain control module will turn the MIL ON by grounding the lamp control circuit. The MIL is OFF if the engine is running correctly.

### Diagnostic Aids

Check for any of the following conditions:

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

• | Check for a faulty Main Relay if MIL is not ON, and the engine cranks but will not start.

• | Check for a short in the 5-volt reference circuit if the MIL is not ON, and the engine cranks but will not start.

• | Check for 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

• | Improper mating of terminals

• | Broken electrical connector locks

• | Improperly formed terminals or damaged terminals

• | A faulty terminal to wire connections

• | Physical damage to the wiring harness

• | A broken wire inside the insulation

• | Corrosion of electrical connections, of electrical splices, or of electrical 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 store the Freeze Frame data on the scan tool, if applicable. This creates an electronic copy of the data that was stored when the fault occurred. The information is stored in the scan tool for later reference.

2. This step will verify if the MIL circuit is the fault or if the PCM is not providing a ground path for the MIL circuit.

3. This step will verify the condition of the MIL control circuit. The PCM is providing the ground for the test light.

4. This step checks for an open in the Ignition Positive Voltage circuits from the main relay. The engine may start and run but there will not be MIL control or serial data if the circuit is open between the last 2 circuit splices before the PCM.

5. This step checks for a short to ground in the PCM 5 volt reference circuit. The MIL will be inoperative and the engine will not start or run if the reference voltage circuit is shorted to ground. Use the 5 volt reference circuit in order to check the circuit wiring, the sensors, and the components for shorts to ground.

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 | Check for an open in the following fuses:

• | IGN-COIL fuse

• | Fuel injector fuse

Was an open fuse found?

--

Go to Step 20

Go to Step 3

3 | Attempt to start the engine. Does the engine start? | -- | Go to Step 4 | Go to Step 10
4 | Install a scan tool, and select the data display. Does the scan tool display any data? | -- | Go to Step 5 | Go to Step 10
5 |

1. Disconnect the PCM electrical connector C1.
2. Back out the PCM terminal C1-17.
3. Jump the C1-17 circuit to ground using a fused jumper wire.
4. Turn ON the ignition, leaving the engine OFF.
5. Observe the MIL.

Does the MIL illuminate?

--

Go to Step 18

Go to Step 6

6 |

1. Turn ON the ignition, leaving the engine OFF.
2. Use a test lamp using the 5 volt reference circuit in order to backprobe the IPC connector terminal C1-2 on the harness side.

Does the test lamp illuminate?

--

Go to Step 7

Go to Step 8

7 |

1. Disconnect the C1 electrical connector from the IPC assembly.
2. Use a test lamp that is connected to B+ in order to probe terminal C1-4 of the IPC assembly on the harness side .
3. Turn the ignition switch to ON, then to OFF while observing the test lamp.

Does the test lamp illuminate with the ignition switch turned on, and then turn OFF when the ignition switch is turned OFF?

--

Go to Step 19

Go to Step 9

8 |

1. Repair the open in the BLK/WHT wire between the junction block and the IPC assembly.
2. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 21

--

9 |

1. Locate and repair the open in the PPL/YEL wire between the I/P cluster assembly and the PCM.
2. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 21

--

10 |

1. Turn ON the ignition, leaving the engine OFF.
2. Use a test lamp that is connected to ground in order to backprobe the PCM connector terminals C1- 2 and C1- 15 .

Does the test light illuminate at each terminal?

--

Go to Step 11

Go to Step 13

11 | Use a test lamp that is connected to ground in order to backprobe the PCM connector terminal C3-20 . Does the test light illuminate? | -- | Go to Step 14 | Go to Step 12
12 | Repair the open in the ignition positive voltage circuit between the IG-COIL fuse and the PCM. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 21 | --
13 |

1. Check for an open in the ignition positive voltage circuit between the main relay and the PCM.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 21

Go to Main Relay Circuit Diagnosis

14 |

1. Turn ON the ignition, leaving the engine OFF.
2. Use a DMM that is connected to ground in order to backprobe the PCM reference voltage terminal C2-1.

Was the measured voltage at the specified value?

5 volts

Go to Step 18

Go to Step 15

15 |

1. Check for a short to ground in the reference voltage circuit and in the circuit components.
2. Repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Was a repair necessary?

--

Go to Step 21

Go to Step 16

16 |

1. Disconnect the PCM connector terminal C1.
2. Use a test lamp that is connected to B+ in order to probe the PCM ground terminals .

Does the test light illuminate at each terminal?

--

Go to Step 18

Go to Step 17

17 | Repair the open in the PCM ground circuits between the PCM and the G104 ground. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 21 | --
18 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | Go to Step 21 | --
19 |

1. Check for any of the following conditions:

• | A faulty bulb

• | A faulty I/P circuit from connector C1 to the MIL bulb socket

• | A faulty electrical connection in the I/P cluster assembly

2. Repair as necessary.

Is the action complete?

--

Go to Step 21

--

20 | Repair the short to ground in the IG-COIL fuse or in the FI fuse circuits. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | Go to Step 21 | --
21 |

1. Turn ON the ignition, leaving the engine OFF.
2. Observe the MIL.
3. Start the engine while continuing to observe the MIL.

Does the MIL illuminate with the ignition ON, and turn OFF after the engine is started?

--

System OK

Go to the Applicable Diagnostic Table