GM Service Manual Online
For 1990-2009 cars only

Refer to Engine Controls Schematics .

Circuit Description

When the ignition switch is initially turned to the run position, the malfunction indicator lamp (MIL) will be ON steady. When the engine is running and there are no active type A or B DTCs stored, the Vehicle Control Module (VCM) turns OFF the MIL. The ignition switch supplies battery voltage directly to the MIL through the gauge fuse. The VCM controls the MIL by providing a ground path through the MIL control circuit in order to turn ON the MIL.

Diagnostic Aids

An open gauge fuse will cause the entire IP cluster to be inoperative.

Check for any circuitry that is suspected of causing an intermittent complaint for the following conditions:

    • Backed out terminals
    • Improper mating
    • Broken locks
    • Improperly formed or damaged terminals
    • Poor terminal to wiring connections
    • Physical damage to the wiring harness

Test Description

The numbers below refer to step numbers on the diagnostic table.

  1. The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame and failure records data with the scan tool if applicable. This creates an electronic copy of the data when the fault occurred. The information is then stored in the scan tool for later reference.

  2. If the engine fails to start and the MIL is inoperative, then the fault can be isolated to either the VCM ignition feed (ECM-I fuse), the battery feed (ECM-BATT fuse), a poor VCM ground at the engine block, or the VCM.

  3. A MIL that responds correctly to the scan tool commands indicates that the fault is not present at this time or that the condition that caused the No MIL condition has been corrected.

  4. This step isolates a VCM problem from a circuit problem.

  5. Locate and repair any shorts that may have caused the fuse to open before replacing the fuse.

  6. This step checks the MIL control circuit for a short to voltage.

  7. For MIL bulb replacement procedures, refer to the appropriate service manual.

  8. For IP replacement procedures, refer to the appropriate service manual.

  9. VCM grounds will only cause a problem if all of the grounds are not making a good connection. If a VCM ground problem is suspected, the most probable place to check is where all the grounds meet at the engine block.

Step

Action

Value(s)

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

  1. Turn the engine OFF for 15 seconds.
  2. Turn the ignition ON, engine OFF.

Is the MIL ON?

--

Go to Step 4

Go to Step 3

3

Attempt to start the engine.

Does the engine start?

--

Go to Step 6

Go to Step 7

4

  1. Install a scan tool.
  2. Command the MIL ON and OFF.

Does the MIL turn ON and OFF when commanded?

--

Go to Step 25

Go to Step 5

5

  1. Turn OFF the ignition.
  2. Disconnect the black VCM connector.
  3. Turn ON the ignition.

Is the MIL on?

--

Go to Step 19

Go to Step 11

6

  1. Turn OFF the ignition.
  2. Disconnect the black VCM connector.
  3. Turn ON the ignition.
  4. Probe the MIL control circuit with a fused jumper connected to ground.

Is the MIL ON?

--

Go to Step 11

Go to Step 8

7

Inspect fuses #9 (ECM-BATT) and #10 (ECM-I) for an open.

Are the fuses OK?

--

Go to Step 9

Go to Step 10

8

Did the fuse in the fused jumper open?

--

Go to Step 13

Go to Step 14

9

  1. Turn OFF the ignition.
  2. Disconnect the black VCM connector.
  3. Turn ON the ignition.
  4. Probe the VCM ignition feed circuit (terminal BK18) with a test light to a ground.

Does the test light illuminate?

--

Go to Step 18

Go to Step 20

10

  1. Check for a short to ground in the circuit of the fuse that was open and repair if necessary.
  2. Replace the faulty fuse.

Is the action complete?

--

Go to Step 25

--

11

Check for faulty VCM connections.

Was a problem found?

--

Go to Step 23

Go to Step 24

12

Repair the open in the VCM ignition feed circuit. Refer to Wiring Repairs in Engine Electrical.

Is the action complete?

--

Go to Step 25

--

13

Repair the short to voltage in the MIL control circuit. Refer to Wiring Repairs in Engine Electrical.

Is the action complete?

--

Go to Step 25

--

14

Check for an open in the MIL control circuit.

Is the action complete?

--

Go to Step 23

Go to Step15

15

Check for an open ignition feed circuit or fuse (gauge #4) to the MIL.

Was a problem found?

--

Go to Step 23

Go to Step 16

16

Check for an open MIL bulb.

Was a problem found?

--

Go to Step 23

Go to Step 17

17

Replace the IP. Refer to the appropriate service manual.

Is the action complete?

--

Go to Step 25

--

18

  1. Turn the ignition off.
  2. Disconnect the gray VCM connector.
  3. Probe the battery feed circuit (terminal GR21) with a test light connected to ground.

Does the test light illuminate?

--

Go to Step 21

Go to Step 22

19

Repair the short to ground in the MIL control circuit.

Is the action complete?

--

Go to Step 25

--

20

Repair the open in the VCM ignition feed circuit.

Is the action complete?

--

Go to Step 25

--

21

Check for a faulty VCM ground connection at the engine block.

Was a problem found?

--

Go to Step 23

Go to Step 11

22

Repair the open battery feed circuit.

Is the action complete?

--

Go to Step 25

--

23

Repair as necessary.

Is the action complete?

--

Go to Step 25

--

24

Replace the VCM.

Important: If the VCM is faulty, reprogram the VCM. Refer to VCM Replacement/Programming .

Is the action complete?

--

Go to Step 25

--

25

  1. Allow engine to idle until normal operating temperature is reached.
  2. Check if there are any DTCs set.

Are any DTCs displayed that have not been diagnosed?

--

Go to The Applicable DTC Table

System OK