GM Service Manual Online
For 1990-2009 cars only

Circuit Description

When the ignition is turned ON, the malfunction indicator lamp (MIL) will be turned ON and remain ON until the engine is running, if no diagnostic trouble codes (DTCs) are stored. Battery voltage is supplied through the ignition switch directly to the MIL telltale. The engine control module (ECM) controls the MIL by providing a ground path through the MIL control circuit to turn ON the MIL.

Diagnostic Aids

An open ignition fuse F4 will cause the entire cluster to be inoperative.

Inspect the battery and ignition feed circuits for poor connections if the MIL is intermittent.

Any circuitry that is suspected as causing an intermittent complaint should be thoroughly inspected for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, poor terminal-to-wiring connections, or physical damage to the wiring harness.

Step

Action

Yes

No

1

Attempt to start the engine.

Does the engine start?

Go to Step 2

Go to Engine Cranks but Does Not Run

2

  1. Turn the ignition switch to LOCK.
  2. Disconnect the engine control module (ECM) connector.
  3. Turn the ignition switch to ON.
  4. Connect a test light between the ECM connector terminal K64 and ground.

Is the test light illuminated?

Go to Step 3

Go to Step 6

3

Inspect terminals for damage or poor connection.

Is a repair necessary?

Go to Step 5

Go to Step 4

4

Replace the ECM. Refer to Engine Control Module Replacement .

Did you complete the replacement?

Go to Diagnostic System Check - Engine Controls

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5

Repair any damaged terminals or poor connection.

Did you complete the repair?

Go to Diagnostic System Check - Engine Controls

--

6

Inspect the fuse F4.

Is the fuse open?

Go to Step 7

Go to Step 8

7

  1. Inspect for a short to ground in the circuit and repair as needed.
  2. Replace the fuse F4.

Did you find and correct the condition?

Go to Diagnostic System Check - Engine Controls

--

8

  1. Inspect for an open circuit between fuse F4 and the ECM connector terminal K64 and repair as needed.
  2. Inspect the MIL bulb and replace if open.

Did you find and correct the condition?

Go to Diagnostic System Check - Engine Controls

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