GM Service Manual Online
For 1990-2009 cars only

Circuit Description

The engine control module (ECM) turns the MIL ON by sending a message on the CAN circuit.

MIL Operation

The MIL is located on the instrument panel cluster (IPC).

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 ECM.

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.

Step

Action

Values

Yes

No

Schematic Reference: Engine Controls Schematics

Connector End View Reference: Engine Control Module Connector End Views or Engine Controls Connector End Views

1

Did you perform the Diagnostic System Check-Engine Controls?

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Go to Step 2

Go to Diagnostic System Check - Engine Controls

2

Did you perform the Diagnostic System Check-Instrument Cluster in Instrument Panel, Gages, and Console?

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Go to Step 3

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

3

Are there any UXXXX DTCs present?

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Go to Diagnostic Trouble Code (DTC) List in Data Link Communications

Go to Step 4

4

Replace the IPC. Refer to Instrument Cluster Replacement in Instrument Panel, Gages, and Console.

Did you complete the replacement?

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Go to Step 5

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5

  1. Remove all test equipment.
  2. Connect any disconnected components or any disconnected fuses.
  3. Turn OFF the ignition for 30 seconds.
  4. Start the engine and operate the vehicle performance, and driveability.
  5. Observe the MIL, the vehicle performance, and the drivebility.

Does the vehicle operate correctly, without any MIL illumination and without any stored DTCs?

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System OK

Go to Diagnostic Trouble Code (DTC) List