For 1990-2009 cars
Engine Controls Components
Power, Ground, MIL, DLC
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

There should always be a steady MIL with the ignition ON and the engine stopped. Ignition feed voltage is supplied directly to the MIL bulb. The Powertrain Control Module (PCM) turns the MIL ON by grounding the MIL driver circuit. No MIL with the key ON, engine not running and DTC P1641 set suggests an open in the MIL driver circuit.

### Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check for the following items:

• | Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness.

• | If the engine runs OK, check for a faulty light bulb, an open in the MIL driver circuit, or an open in the instrument cluster ignition feed.

• | If the engine cranks but will not run, check for an open PCM ignition or battery feed or a poor PCM to engine ground.

### Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table:

1. A no MIL condition accompanied by a no start condition suggests a faulty PCM ignition feed or battery feed circuit.

2. Using a test light connected to battery positive voltage, probe each of the PCM ground terminals to ensure that a good ground is present. Refer to Engine Controls Component Views for terminal locations of the PCM ground circuits.

3. This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

#### No Malfunction Indicator Lamp (MIL)

Step | Action | Value(s) | Yes | No
--- | --- | --- | --- | ---
1 | Did you perform the Powertrain OBD System Check? | -- | Go to Step 2 | Go to the Powertrain On Board Diagnostic (OBD) System Check
2 | Attempt to start the engine. Does the engine start? | -- | Go to Step 3 | Go to Step 6
3 | Inspect the fuse for the instrument cluster ignition feed circuit. Is the fuse OK? | -- | Go to Step 4 | Go to Step 15
4 |

1. Turn on the ignition switch.
2. Use a test lamp in order to probe the ignition feed circuit between the cluster connector and ground.

Is the test lamp on?

--

Go to Step 5

Go to Step 12

5 |

1. Turn off the ignition switch.
2. Disconnect the powertrain control module (PCM).
3. Turn on the ignition switch.
4. Jumper the malfunction indicator lamp (MIL) driver circuit between the PCM connector and ground.
5. Observe the MIL.

Is the MIL ON?

--

Go to Step 10

Go to Step 11

6 | Inspect the PCM ignition feed fuse and the battery feed fuse. Are both of the fuses OK? | -- | Go to Step 7 | Go to Step 14
7 |

1. Turn off the ignition switch.
2. Disconnect the PCM.
3. Turn on the ignition.
4. Use a test lamp in order to probe the ignition feed circuit between the PCM harness connector and ground.

Is the test lamp on?

--

Go to Step 8

Go to Step 13

8 | Use a test lamp in order to probe the battery feed circuit between the PCM harness connector and ground. Is the test lamp on? | -- | Go to Step 9 | Go to Step 13
9 |

1. Test for a faulty PCM ground or a faulty PCM ground connection.
2. Repair the circuit or the connection as necessary. Refer to Wiring Repairs in Wiring Systems.

Is the circuit OK?

--

Go to Step 10

Go to Powertrain On Board Diagnostic (OBD) System Check

10 |

1. Inspect for a faulty connection at the PCM.
2. Repair the connection as necessary. Refer to Connector Repairs in Wiring Systems.

Is the circuit OK?

--

Go to Step 16

Go to Powertrain On Board Diagnostic (OBD) System Check

11 |

1. Inspect the MIL driver circuit for an open.
2. Repair the circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Is the circuit OK?

--

Go to Step 17

Go to Powertrain On Board Diagnostic (OBD) System Check

12 | Repair an open in the ignition feed circuit to the instrument panel indicators. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
13 | Locate and repair an open in the PCM battery feed circuit or the PCM ignition feed circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | ---
14 | Locate and repair a short to ground in the PCM ignition feed circuit or the PCM battery feed circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | ---
15 | Locate and repair a short to ground in the ignition feed circuit of the instrument panel indicators. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
16 | Important: : The replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Replace the PCM. Did you complete the repair? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
17 |

1. Inspect the MIL driver circuit for a faulty connection at the instrument panel connector.
2. Repair the circuit as necessary. Refer to Connector Repairs in Wiring Systems.

Is the MIL driver circuit OK?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

--