GM Service Manual Online
For 1990-2009 cars only

Object Number: 185027  Size: MF
Engine Controls Components
PWR, GND, and DLC
OBD II Symbol Description Notice
Handling ESD Sensitive Parts Notice
Handling ESD Sensitive Parts Notice

Circuit Description

There should always be a steady malfunction indicator lamp (MIL) when the ignition is ON and the engine is OFF. Battery ignition voltage is supplied to the lamp. The PCM will turn the lamp ON by grounding the ignition feed circuit.

Diagnostic Aids

If the engine cranks but will not run, check:

    • Continuous battery-fuse or fusible link for open.
    • PCM ignition fuse for open.
    • Battery Feed circuit to PCM for open.
    • Ignition Feed circuit to PCM for open.
    • Poor connection to PCM.

An intermittent may be caused by any of the following conditions:

    • A poor connection
    • Rubbed through wire insulation
    • A broken wire inside the insulation

Thoroughly check any circuitry that is suspected of causing the intermittent complaint. Refer to Intermittents and Poor Connections Diagnosis in Wiring Systems.

If a repair is necessary, refer to Wiring Repairs or Connector Repairs in Wiring Systems.

Test Description

Number(s) below refer to the step number(s) on the Diagnostic Table.

  1. This step will isolate the problem in the MIL control circuit.

  2. If the Battery Feed, Ignition Feed and Diagnostic Test circuits have voltage, the PCM connections, grounds, or PCM are malfunctioning.

  3. Refer to Powertrain Control Module Connector End Views for PCM pin locations of ground circuits.

  4. If the fuse/fusible link is open, refer to PCM Wiring Diagram for complete circuit.

Step

Action

Value(s)

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic System check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Attempt to start the engine.

Does the engine start?

--

Go to Step 3

Go to Step 6

3

Check the fuse number 4.

Is the fuse OK?

--

Go to Step 4

Go to Step 14

4

Turn ON the ignition, probe the ignition feed circuit at the cluster connector with an J 35616-200 unpowered test lamp connected to ground.

Does the test light illuminate?

--

Go to Step 5

Go to Step 11

5

  1. Turn OFF the Ignition.
  2. Disconnect the blue PCM connector.
  3. Turn ON the ignition.
  4. With a fused jumper wire connected to ground, probe the MIL control circuit at the PCM connector.
  5. Observe the MIL.

Is the MIL ON?

--

Go to Step 9

Go to Step 10

6

Check the PCM Ignition Feed and Battery Feed fuses.

Are both of the fuses OK?

--

Go to Step 7

Go to Step 13

7

  1. Turn OFF the ignition.
  2. Disconnect the PCM connectors.
  3. Turn ON the ignition.
  4. Probe the PCM harness ignition and battery feed circuits with an J 35616-200 unpowered test lamp connected to ground.

Is the test light ON both circuits?

--

Go to Step 8

Go to Step 12

8

  1. Check for a proper PCM ground or a proper PCM ground connection.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you perform a repair?

--

Go to Step 20

Go to Step 9

9

  1. Check for a proper connection at the PCM.
  2. If a poor connection is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

DId you perform a repair?

--

Go to Step 20

Go to Step 15

10

  1. Check the MIL control circuit for an open.
  2. If the MIL control circuit is open, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

Did you perform a repair?

--

Go to Step 20

Go to Step 16

11

Repair the open in the ignition feed circuit to the cluster connector. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 20

--

12

Locate and repair open in the PCM battery feed circuit or the PCM ignition feed circuit as necessary . Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 20

--

13

Locate and repair short to ground in the PCM ignition feed circuit or the PCM Battery Feed circuit as necessary. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 20

--

14

Locate and repair short to ground in the instrument cluster ignition feed circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?

--

Go to Step 20

--

15

Replace the PCM.

Important: The new PCM must be programmed. Refer to Powertrain Control Module Replacement/Programming .

Is the action complete?

--

Go to Step 20

--

16

  1. Check the MIL control circuit for a proper connection at the instrument cluster connector.
  2. If a problem is found, repair as necessary. Refer to Wiring Repairs in Wiring Systems.

DId you perform a repair?

--

Go to Step 20

Go to Step 17

17

  1. Remove the instrument cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges and Console.
  2. Inspect the MIL bulb.

Is the bulb OK?

--

Go to Step 19

Go to Step 18

18

Replace the MIL bulb.

Is the action complete?

--

Go to Step 20

--

19

Replace the instrument cluster. Refer to Instrument Cluster Replacement in Instrument Panel, Gauges and Console.

Is the action complete?

--

Go to Step 20

--

20

  1. Using the scan tool, select DTC, Clear Info.
  2. Attempt to start the engine.

Does the engine start and continue to run?

--

Go to Step 21

Go to Step 2

21

  1. Allow the engine to idle until normal operating temperature is reached.
  2. Select DTC, Failed This Ign.

Are any DTCs displayed?

--

Go to the Applicable DTC Table

Go to Step 22

22

Using the scan tool, select Capture Info, Review Info.

Are any DTCs displayed that have not been diagnosed?

--

Go to the Applicable DTC Table.

System OK