GM Service Manual Online
For 1990-2009 cars only

Diagnostic Aids

Inspect the CRANK, PCM 1, and PCM B fuses for opens.

Step

Action

Yes

No

Schematic References: Starting and Charging Schematics and Engine Controls Schematics

Connector End View Reference: Engine Electrical Connector End Views

1

Did you preform the Engine Electrical Diagnostic System Check?

Go to Step 2

Go to Diagnostic System Check - Engine Electrical

2

Turn the ignition switch to the START position.

Does the engine crank?

Go to Testing for Intermittent Conditions and Poor Connections in Wiring Systems

Go to Step 3

3

Turn the ignition switch to the START position.

Does the starter relay click?

Go to Step 14

Go to Step 4

4

Is the vehicle equipped with a manual transmission?

Go to Step 5

Go to Step 7

5

  1. Install a scan tool.
  2. Turn ON the ignition, with the engine OFF.
  3. With a scan tool, observe the Clutch Pedal Switch parameter in the PCM data list while pressing the clutch pedal.

Does the scan tool display Applied?

Go to Step 7

Go to Step 6

6

  1. Turn OFF the ignition.
  2. Disconnect the powertrain control module (PCM) harness connector.
  3. Connect a test lamp between the clutch start switch signal of the PCM harness and a good ground.
  4. Turn the ignition to the START position while pressing the clutch pedal.

Does the test lamp illuminate?

Go to Step 7

Go to Step 11

7

  1. Turn OFF the ignition.
  2. Disconnect the powertrain control module (PCM) harness connector.
  3. Connect a test lamp between the Crank Voltage circuit of the PCM harness and a good ground.
  4. With the transmission in park, or clutch pedal pressed, turn the ignition switch to the START position.

Does the test light illuminate?

Go to Step 10

Go to Step 8

8

Inspect for poor connections at the PCM connector, Underhood Fuse Block or ignition switch harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 32

Go to Step 9

9

Test the supply voltage circuit of the crank voltage circuit and Crank fuse for an open or high resistance. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 32

Go to Step 24

10

  1. Turn OFF the ignition.
  2. Disconnect the PCM harness connector.
  3. Connect a DMM between the starter enable relay control circuit of the PCM harness and a good ground.
  4. Turn the ignition to the START position.

Does the DMM measure approximately 12 volts?

Go to Step 22

Go to Step 11

11

  1. Remove the starter relay.
  2. Connect a test light from the supply voltage circuit of the starter relay coil circuit to ground.
  3. With the transmission in park, or clutch pedal pressed, turn the ignition switch to the START position.

Does the test light illuminate?

Go to Step 12

Go to Step 13

12

  1. Reconnect the PCM.
  2. Connect a test light from the supply voltage circuit of the starter motor relay coil circuit to the control circuit of the starter motor relay coil circuit.
  3. With the transmission in park, or clutch pedal pressed, turn the ignition switch to the START position.

Does the test light illuminate?

Go to Step 20

Go to Step 17

13

  1. Turn OFF the ignition.
  2. Disconnect the park neutral position (PNP) switch. Refer to Park/Neutral Position Switch Replacement in Automatic Transmission - 4L60-E/4L65-E, Park/Neutral Position Switch Replacement in Automatic Transmission - 4L80-E/4L85-E, Park/Neutral Position Switch Replacement in Automatic Transmission - Allison, or Clutch Pedal Engine Start Switch Replacement in Clutch.
  3. Turn ON the ignition, with the engine OFF.
  4. Connect a 10-amp fused jumper between the starter motor relay coil control circuits of the PNP switch or clutch pedal position switch.
  5. With the transmission in PARK, or clutch pedal pressed, turn the ignition switch to the START position.

Does the test lamp illuminate?

Go to Step 21

Go to Step 18

14

  1. Turn OFF the ignition.
  2. Disconnect the starter relay.
  3. Connect a test lamp between the battery positive voltage circuit of the starter motor relay switch circuit and a good ground.

Does the test lamp illuminate?

Go to Step 15

Go to Step 26

15

Connect a 30-amp fused jumper between the battery positive voltage circuit of the starter relay switch circuit and the supply voltage circuit of the starter solenoid.

Does the engine crank?

Go to Step 20

Go to Step 16

16

Does the fuse in the jumper open?

Go to Step 27

Go to Step 19

17

Test the control circuit of the starter motor relay for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 32

Go to Step 22

18

Repair open or high resistance on the supply voltage circuit of the starter motor relay coil circuit. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 32

--

19

Test the supply voltage circuit of the starter solenoid for an open or high resistance. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 32

Go to Step 25

20

Inspect for poor connections at the starter motor relay. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 32

Go to Step 28

21

    • If equipped with an automatic transmission, inspect for poor connection at the PNP switch harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems. If OK, perform the Park/Neutral Position Switch Adjustment in Automatic Transmission - 4L60-E/4L65-E, Park/Neutral Position Switch Adjustment in Automatic Transmission - 4L80-E/4L85-E, or Park/Neutral Position Switch Adjustment in Automatic Transmission - Allison.
    • If equipped with a manual transmission, inspect for poor connection at the clutch pedal position switch harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 32

Go to Step 29

22

Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 32

Go to Step 23

23

Important: The replacement PCM must be programmed.

Replace the PCM/engine control module (ECM). Refer to Powertrain Control Module Replacement in Engine Controls - 4.3L, Powertrain Control Module Replacement in Engine Controls - 4.8L, 5.3L, and 6.0L, Powertrain Control Module Replacement in Engine Controls - 8.1L, or Engine Control Module Replacement in Engine Controls - 6.6L.

Is action complete?

Go to Step 32

--

24

Inspect for poor connections at the ignition switch harness connector. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 32

Go to Step 30

25

Inspect for poor connections at the starter solenoid. Refer to Testing for Intermittent Conditions and Poor Connections and Connector Repairs in Wiring Systems.

Did you find and correct the condition?

Go to Step 32

Go to Step 31

26

Repair the open or high resistance in the battery positive voltage circuit of the Starter relay switch circuit. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 32

--

27

Repair the short to ground in the supply voltage circuit of the starter solenoid. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?

Go to Step 32

--

28

Replace the Starter Relay. Refer to Relay Replacement in Wiring Systems.

Did you complete the replacement?

Go to Step 32

--

29

  1. Replace the PNP switch. Refer to Park/Neutral Position Switch Replacement in Automatic Transmission - 4L60-E/4L65-E, Park/Neutral Position Switch Replacement in Automatic Transmission - 4L80-E/4L85-E, or Park/Neutral Position Switch Replacement in Automatic Transmission - Allison.
  2. Replace the clutch pedal position switch. Refer to Clutch Pedal Engine Start Switch Replacement in Clutch.

Did you complete the replacement?

Go to Step 32

--

30

Replace the ignition switch. Refer to Ignition and Start Switch Replacement in Steering Wheel and Column.

Did you complete the replacement?

Go to Step 32

--

31

Replace the starter. Refer to Starter Motor Replacement .

Did you complete the replacement?

Go to Step 32

--

32

Operate the system for which the symptom occurred.

Did you correct the condition?

System OK

Go to Step 2