For 1990-2009 cars
Engine Controls Components
Cell 20: MIL Control
OBD II Symbol Description Notice

### Circuit Description

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

### Diagnostic Aids

An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check 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 malfunctioning light bulb, an open in the MIL control 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

Numbers below refer to the Step numbers on the Diagnostic Table:

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

2. Using a test lamp0 connected to B+, probe each of the PCM ground terminals to ensure that a good ground is present.

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.

#### No Malfunction Indicator Lamp (MIL)

Step | Action | Values | Yes | No
--- | --- | --- | --- | ---
1 | Was the Powertrain On-Board Diagnostic (OBD) 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 |

1. Turn ON the ignition switch.
2. Probe the ignition feed circuit at the cluster connector with a test lamp to ground.

Is the test lamp ON?

--

Go to Step 5

Go to Step 12

5 |

1. Turn OFF the ignition switch.
2. Disconnect the PCM.
3. Turn ON the ignition switch.
4. Jumper the MIL control 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 OFF the ignition switch.
2. Disconnect the PCM.
3. Turn ON the ignition switch.
4. Probe the ignition feed circuit at the PCM harness connector with a test lamp to ground.

Is the test lamp ON?

--

Go to Step 8

Go to Step 13

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

1. Check for a malfunctioning PCM ground or a poor PCM ground connection.
2. If a problem is found, repair as necessary. Refer to Repairing Connector Terminals 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 Repairing Connector Terminals 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 control circuit for an open.
2. If the MIL control 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. Refer to Wiring Repairs in Wiring Systems. 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 Wiring Repairs in Wiring Systems. 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 Wiring Repairs in Wiring Systems. 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 Wiring Repairs in Wiring Systems. Is action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
16 | Important:: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
17 |

1. Check the MIL control circuit for a poor connection at the instrument panel connector.
2. If a problem is found, repair as necessary. Refer to Intermittents and Poor Connections Diagnosis .

Was a problem found?

--

Go to Powertrain On Board Diagnostic (OBD) System Check

Go to Instrument Cluster System Check