GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Pontiac 🢒 2001 🢒 Aztek - AWD 🢒 Body and Accessories 🢒 Instrument Panel, Gauges, and Console 🢒 Malfunction Indicator Lamp (MIL) Always On

System Description

The Diagnostic System Check - Engine Controls must be the starting point for any driveability complaint diagnosis. Perform a careful visual and physical inspection of the powertrain control module (PCM) and engine grounds for being clean and tight. Refer to Visual and Physical Check in Symptoms - Engine Controls . The Diagnostic System Check - Engine Controls is an organized approach to identifying a problem created by an electronic engine control system malfunction.

The powertrain control module (PCM) controls the malfunction indicator lamp (MIL) by providing a ground path through the MIL control circuit to turn ON the MIL. When the ignition is turned ON, the MIL will remain ON until the engine is running, if no diagnostic trouble codes (DTC) are stored. If the MIL is illuminated, then the engine stalls, the MIL will remain illuminated so long as the ignition is ON.

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 the 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:

    • 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

Test Description

The number below refers to the step number on the diagnostic table.

  1. Using a test lamp connected to battery positive voltage, probe the MIL control circuit at the PCM.

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

With a scan tool, observe the DTCs.

Are any DTCs set?

Go to applicable DTCs

Go to Step 3

3
  1. Turn OFF the ignition.
  2. Observe the MIL on the instrument panel (IP) cluster.

Is the MIL ON?

Go to Step 6

Go to Step 4

4
  1. Install a scan tool.
  2. Command the MIL ON and OFF several times while monitoring the IP cluster.

Does the MIL turn ON and OFF when commanded?

Go to Diagnostic Aids

Go to Step 5

5

Test the MIL control circuit for a short to ground. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 7

--

6

Test the MIL control circuit for a short to voltage. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 7

--

7
  1. Install a scan tool.
  2. Command the MIL ON and OFF several times while monitoring the IP cluster.

Does the MIL turn OFF when commanded?

Go to Diagnostic System Check - Engine Controls

Go to Step 2