For 1990-2009 cars
Engine Controls Components
Cell 21: Power, Ground, MIL, and DLC
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

### Circuit Description

The Powertrain On Board Diagnostic (OBD) System Check must be the starting point for any driveability complaint diagnosis. Before using this procedure, you should perform a careful visual/physical check of the PCM and engine grounds for being clean and tight. Refe to Visual/Physical Check in Intermittent Conditions . The Powertrain On Board Diagnostic (OBD) System Check is an organized approach to identifying a problem created by an electronic engine control system malfunction. No MIL with the key on, engine not running and DTC P1671 Malfunction Indicator Lamp (MIL) Control Circuit 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.Refer to Intermittents and Poor Connections Diagnosis and Connector Repairs

• | If the engine runs OK, check for a faulty lamp 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. Refer to Wiring Repairs .

### 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 battery positive voltage, 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 | Turn the 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. Turn the ignition OFF.
2. Disconnect the PCM.
3. Turn the 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. Turn the ignition OFF.
2. Disconnect the PCM.
3. Turn the 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 Wiring Repairs in Wiring Systems.

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 Wiring Repairs in Wiring Systems.

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 Wiring Repairs in Wiring Systems.

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. Is the 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. Is the 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. Is the 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. Is the action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
16 | Important: Replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is the 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 Wiring Repairs in Wiring Systems.

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Diagnostic System Check - Instrument Cluster in Instrument Panel, Gauges and Console