For 1990-2009 cars

### Circuit Description

There should be a steady malfunction indicator lamp (MIL) with the ignition ON and the engine OFF. 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 suggests an open in the battery positive and ignition positive voltage feed fuses and circuits.

### MIL Operation

The 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 diagnostic trouble code (DTC) will be stored if a MIL is requested by the diagnostic.

#### MIL Illumination

• | The MIL will illuminate with ignition 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.

#### Diagnostic System Check-Engine Controls

Perform the Diagnostic System Check - Engine Controls , when the following conditions are present:

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

• | The MIL remains ON while the engine is running

• | The MIL is flashing while the engine is running

• | A driveability symptom is determined

### Diagnostic Aids

Inspect for the following conditions:

• | 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.

• | PCM and engine grounds for clean and secure connections

Step | Action | Yes | No
--- | --- | --- | ---
Schematic Reference: Engine Controls Schematics
1 | Did you perform the Diagnostic System Check-Engine Controls? | Go to Step 2 | Go to Diagnostic System Check - Engine Controls
2 | Attempt to start the engine. Does the engine start? | Go to Step 3 | Go to Step 9
3 | Inspect the fuse supplying voltage to the MIL. Is the fuse open? | Go to Step 7 | Go to Step 4
4 |

1. Turn OFF the ignition.
2. Disconnect the PCM connector containing the MIL control circuit. Refer to Powertrain Control Module Replacement .
3. Turn ON the ignition, with the engine OFF.
4. Probe the MIL control circuit in the PCM harness connector with a fused jumper wire connected to ground. Refer to Using Fused Jumper Wires in Wiring Systems.

Is the MIL ON?

Go to Step 15

Go to Step 5

5 |

1. Turn OFF the ignition.
2. Remove the instrument panel (IP). Refer to Instrument Cluster Replacement in Instrument Panel, Gages and Console.
3. Probe the MIL ignition positive voltage circuit at the IP harness connector with a test lamp connected to a good ground.

Is the test lamp illuminated?

Go to Step 6

Go to Step 8

6 | Test the MIL control circuit for an open or high resistance and repair as necessary. Refer to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | Go to Diagnostic System Check - Engine Controls | Go to Step 14
7 | Repair the short to ground in the MIL ignition positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Diagnostic System Check - Engine Controls | --
8 | Repair the open in the MIL ignition positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Diagnostic System Check - Engine Controls | --
9 | Inspect the PCM fuse and the ignition 1 main fuse. Is one or both of the fuses open? | Go to Step 12 | Go to Step 10
10 |

1. Turn OFF the ignition.
2. Disconnect the PCM. Refer to Powertrain Control Module Replacement .
3. Turn ON the ignition, with the engine OFF.
4. Connect a test lamp between the PCM ignition positive voltage circuits and a good ground.

Does the test lamp illuminate while probing ALL PCM ignition positive voltage circuits?

Go to Step 11

Go to Step 12

11 | Connect a test lamp from the PCM battery positive voltage circuit and good ground. Does the test lamp illuminate? | Go to Step 13 | Go to Step 12
12 | Locate and repair the open or short to ground in the PCM ignition feed circuits or the PCM battery positive voltage circuit. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | Go to Diagnostic System Check - Engine Controls | --
13 |

1. Inspect for a poor PCM ground or a poor PCM ground connection. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
2. Repair the condition as necessary. Refer to Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Diagnostic System Check - Engine Controls

Go to Step 15

14 | Inspect for poor connections at the IP and repair as necessary. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Diagnostic System Check - Engine Controls | Go to Step 16
15 | Inspect for poor connections at the PCM and repair as necessary. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. Did you find and correct the condition? | Go to Diagnostic System Check - Engine Controls | Go to Step 17
16 | Replace the IP. Refer to Instrument Cluster Replacement in Instrument Panel, Gages and Console. Did you complete the replacement? | Go to Diagnostic System Check - Engine Controls | --
17 | Replace the PCM. Refer to Powertrain Control Module Replacement . Did you complete the replacement? | Go to Diagnostic System Check - Engine Controls | --