For 1990-2009 cars
Engine Controls Components
Engine Controls Schematics
OBD II Symbol Description Notice
Handling ESD Sensitive Parts 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. 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 the MIL DTC set suggests an open in the MIL control circuit.

### MIL Operation

The Malfunction Indicator Lamp (MIL) is located on the instrument panel and is displayed as CHECK ENGINE lamp.

#### MIL Function

• | The MIL informs the driver that a malfunction has occurred and the vehicle should be taken in for service as soon as possible

• | The MIL illuminates during a bulb test and a system test

• | A DTC will be stored if a MIL is requested by the diagnostic

#### MIL Illumination

• | The MIL will illuminate with ignition switch ON and the engine not running

• | The MIL will turn OFF when the engine is started

• | The MIL will remain ON if the self-diagnostic system has detected a malfunction

• | The MIL may turn OFF if the malfunction is not present

• | If the MIL is illuminated and then the engine stalls, the MIL will remain illuminated so long as the ignition switch is ON.

• | If the MIL is not illuminated and the engine stalls, the MIL will not illuminate until the ignition switch is cycled OFF, then ON.

#### Powertrain On Board Diagnostic (OBD) System Check

Perform the Powertrain On Board Diagnostic (OBD) System Check, when the following conditions are present:

• | When the MIL does not turn ON when the ignition switch is turned to the RUN position. See above for MIL Operation

• | When the MIL remains ON while the engine is running

• | When the MIL is flashing while the engine is running

• | When a driveability symptom is determined

### Diagnostic Aids

Inspect the following items:

• | If the engine runs OK, inspect for a malfunctioning MIL, an open in the MIL control circuit, or an open in the instrument cluster ignition feed.

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

Many situations may lead to an intermittent condition. Perform each inspection or test as directed.

Important: : Remove any debris from the connector surfaces before servicing a component. Inspect the connector gaskets when diagnosing or replacing a component. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion.

• | Loose terminal connection

- | Use a corresponding mating terminal to test for proper tension. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

- | Inspect the harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and faulty terminal to wire connection. Refer to Testing for Intermittent Conditions and Poor Connections , and to Connector Repairs in Wiring Systems for diagnosis and repair.

• | Damaged harness--Inspect the wiring harness for damage. If the harness inspection does not reveal a problem, observe the display on the scan tool while moving connectors and wiring harnesses related to the sensor. A change in the scan tool display may indicate the location of the fault. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

• | Inspect the powertrain control module (PCM) and the engine grounds for clean and secure connections. Refer to Wiring Repairs in Wiring Systems for diagnosis and repair.

If the condition is determined to be intermittent, reviewing the Snapshot or Freeze Frame/Failure Records may be useful in determining when the DTC or condition was identified.

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 lamp connected to battery positive voltage, 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 | 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 | 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.
2. Probe the ignition feed circuit at the cluster connector with a test lamp to ground.

Does the test lamp illuminate?

--

Go to Step 5

Go to Step 12

5 |

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Turn ON the ignition, with the engine OFF.
4. Jumper the MIL driver circuit at the PCM connector to ground and observe the MIL.

Is the MIL illuminated?

--

Go to Step 10

Go to Step 11

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

1. Turn OFF the ignition.
2. Disconnect the PCM.
3. Turn ON the ignition, with the engine OFF.
4. Probe the ignition feed circuits at the PCM harness connector with a test lamp to ground.

Does the test lamp illuminate while probing all PCM feed circuits?

--

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. Does the test lamp illuminate? | -- | Go to Step 9 | Go to Step 13
9 | Inspect for a faulty PCM ground or a poor PCM ground connection. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | Go to Step 10
10 | Inspect for a poor connection at the PCM. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | Go to Step 16
11 |

1. Test 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.

Did you find and correct the condition?

--

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. Did you find and correct the condition? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
13 | Locate and repair open in PCM battery feed circuits or PCM ignition feed circuits as necessary. Refer to Wiring Repairs in wiring systems. Did you find and correct the condition? | -- | 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. Did you find and correct the condition? | -- | 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. Did you find and correct the condition? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
16 | Important:: The replacement PCM must be programmed. Replace the PCM. Go to Powertrain Control Module Replacement/Programming Did you complete the replacement? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | --
17 | Test the MIL driver circuit for a poor connection at the instrument panel connector. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Powertrain On Board Diagnostic (OBD) System Check | Go to Step 3