The engine control module (ECM) controls engine cranking based on a power mode input and the status of the park/neutral position (PNP) switch. With the transmission in Park/Neutral, voltage at the ECM PNP switch signal circuit is high. This indicates to the ECM that conditions are acceptable for cranking. When a crank request power mode is seen, the ECM applies ground to the starter relay coil control circuit. This energizes the coil side of the relay, which pulls the switch side of the relay closed, applying voltage to the starter terminal A (4.2L) or S (5.3L) and engaging the starter solenoid.

Schematic Reference

Connector End View Reference

Component Connector End Views

Description and Operation

Starting System Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

1. Ignition ON, transmission in Park. Observe the scan tool ECM PNP Switch parameter. The reading should be Park/Neutral.

⇒	If not the specified value, refer to PNP Switch Circuit Malfunction.

2. Command the Starter Relay ON with the scan tool, or turn the ignition switch to the START position. The starter solenoid should engage and the engine should crank.

⇒	If the solenoid does not engage, refer to STRTR Relay Circuit Malfunction.

⇒	If the solenoid engages but the engine does not crank, refer to Starter Solenoid Clicks, Engine Does Not Crank .

PNP Switch Circuit Malfunction

1. Inspect the range selector lever cable for proper adjustment. Refer to Range Selector Lever Cable Adjustment .
2. Inspect the park/neutral position switch for proper adjustment. Refer to Park/Neutral Position Switch Adjustment .
3. Ignition OFF, disconnect the harness connector at the park/neutral position switch. Refer to Park/Neutral Position Switch Replacement .
4. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 12 and ground.

⇒	If the test lamp does not illuminate, test the ignition circuit for an open/high resistance.

5. Ignition ON and park/neutral position switch disconnected, observe the scan tool ECM PNP Switch parameter. The reading should be In Gear.

⇒	If not the specified value, test the signal circuit terminal 1 for a short to voltage. If the circuit tests normal, replace the ECM.

6. Install a 3A fused jumper wire between the ignition circuit terminal 12 and the signal circuit terminal 1. Verify that the scan tool PNP Switch parameter is Park/Neutral.

⇒	If not the specified value, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

7. If all circuits test normal, test or replace the park/neutral position switch.

STRTR Relay Circuit Malfunction

1. Ignition OFF, remove the STRTR relay.
2. Verify that a test lamp illuminates between the B+ circuit terminal 87 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

3. Ignition ON, transmission in Park, verify that a test lamp illuminates between the park/neutral signal circuit terminal 86 and ground.

⇒	If the test lamp does not illuminate, test the signal circuit for an open/high resistance.

4. Connect a test lamp between the park/neutral signal circuit terminal 86 and the relay coil control circuit terminal 85.
5. Ignition ON, transmission in Park. Command the Starter Relay ON and OFF with a scan tool, or turn the ignition switch between the START and RUN positions. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the ECM.

⇒	If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

6. Install the STRTR relay.
7. Install a test lamp between the starter terminal A (4.2L) or S (5.3L) and ground.

Important: The engine may begin to crank.

8. Ignition ON, transmission in Park, command the Starter Relay ON with a scan tool, or turn the ignition switch to the START position. The test lamp should illuminate.

⇒	If the test lamp does not illuminate, test the relay controlled output circuit for an open/high resistance. If the circuit tests normal, test or replace the STRTR relay.

9. If all circuits test normal, test or replace the starter.

PNP Switch

1. Inspect the range selector lever cable for proper adjustment. Refer to Range Selector Lever Cable Adjustment .
2. Inspect the park/neutral position switch for proper adjustment. Refer to Park/Neutral Position Switch Adjustment .
3. Ignition OFF. Disconnect the harness connector from the park/neutral switch. Refer to Park/Neutral Position Switch Replacement .
4. With the PNP switch in the following positions, test for infinite resistance between the ignition terminal 12 and the signal terminal 1.

•

R

•

OD

•

D

•

2

•

1

⇒	If not the specified value, replace the PNP switch.

5. With the PNP switch in the following positions, test for less than 2.0 ohms between the ignition terminal 12 and the signal terminal 1.

•

P

•

N

⇒	If greater than the specified range, replace the PNP switch.

STRTR Relay

1. Ignition OFF, remove the STRTR relay. Refer to Relay Replacement .
2. Test for 60-180 ohms between terminals 85 and 86.

⇒	If not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If not the specified value, replace the relay.

4. Install a 20A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2.0 ohms between terminals 30 and 87.

⇒	If greater than specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.