For 1990-2009 cars

Refer to

#### Power, Ground, MIL, and DLC

Engine Controls Components
Information Sensors
Ignition Controls
OBD II Symbol Description Notice
Handling ESD Sensitive Parts 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

The numbers below refer to the step numbers 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 B+, probe each of the PCM ground terminals to ensure that a good ground is present. Refer to PCM Terminal End View 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 | Was the Powertrain On-Board Diagnostic System Check performed? | -- | Go to Step 2 | Go to 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 | Check the fuse for the instrument cluster ignition feed circuit. Is the fuse OK? | -- | Go to Step 4 | Go to Step 15
4 | Ignition on , probe the ignition feed circuit at the cluster connector with a test light to ground. Is the test light on ? | -- | Go to Step 5 | Go to Step 12
5 |

1. Ignition off .
2. Disconnect the PCM.
3. Ignition on .
4. Jumper the MIL driver circuit at the PCM connector to ground and observe the MIL.

Is the MIL on ?

--

Go to Step 10

Go to Step 11

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

1. Ignition off .
2. Disconnect the PCM.
3. Ignition on .
4. Probe the ignition feed circuit at the PCM harness connector with a test light to ground.

Is the test light on ?

--

Go to Step 8

Go to Step 13

8 | Probe the battery feed circuit at the PCM harness connector with a test light to ground. Is the test light on ? | -- | Go to Step 9 | Go to Step 13
9 |

1. Check for a faulty PCM ground or a poor PCM ground connection.
2. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis Section .

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 10

10 |

1. Check for a poor connection at the PCM.
2. If a poor connection is found, repair it as necessary. Refer to Repair Procedures in Electrical Diagnosis Section .

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 16

11 |

1. Check the MIL driver circuit for an open.
2. If the MIL driver circuit is open, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis Section .

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Step 17

12 | Repair open in the ignition feed circuit to the instrument panel indicators. Refer to Fuse Block Details in Electrical Diagnosis Section . Is action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
13 | Locate and repair open in PCM battery feed circuit or PCM ignition feed circuit as necessary. Refer to Fuse Block Details in Electrical Diagnosis Section . Is action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
14 | Locate and repair short to ground in PCM ignition feed circuit or PCM battery feed circuit as necessary. Refer to Fuse Block Details in Electrical Diagnosis Section . Is action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
15 | Locate and repair short to ground in the instrument panel indicators ignition feed circuit. Refer to Fuse Block Details in Electrical Diagnosis Section . Is action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
16 | Replace the PCM. Important: Replacement PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
17 |

1. Check the MIL driver circuit for a poor connection at the instrument panel connector.
2. If a problem is found, repair as necessary. Refer to Repair Procedures in Electrical Diagnosis Section .

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Instrument Panel in Electrical Diagnosis