When the ignition switch is placed in the START position, a discrete signal is supplied to the body control module (BCM), notifying it that the ignition is in the START position. The BCM sends the power mode to the engine control module (ECM) via the serial data circuit. The engine control module (ECM) controls engine cranking based on the power mode, the status of the park/neutral position (PNP) switch, and other data. With the transmission in Park/Neutral, voltage at the ECM PNP switch signal circuit is low. This indicates to the ECM that conditions are acceptable for cranking. When a power mode crank request is seen, the ECM applies voltage to the STRTR relay coil control circuit. The STRTR relay supplies voltage to the starter terminal B X2, engaging the starter solenoid.

Schematic Reference

Starting and Charging Schematics

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, observe the scan tool ECM PNP Switch parameter while shifting the transmission through each range. The reading should change between Park/Neutral and In Gear.

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

2. Transmission in park, attempt to start the vehicle. The STRTR relay should click and the engine should begin cranking.

⇒	If the crank relay does not click or the engine does not crank, refer to STRTR Relay Circuit Malfunction.

PNP Switch Circuit Malfunction

1. Inspect the range selector lever cable for proper adjustment. Refer to Range Selector Lever Cable Adjustment.
2. Inspect the PNP switch for proper adjustment. Refer to Park/Neutral Position Switch Adjustment.
3. Ignition OFF. Disconnect the harness connector at the PNP 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 a a short to ground or an open/high resistance.

5. Verify the scan tool ECM PNP Switch parameter is 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 signal circuit terminal 1 and the ignition circuit terminal 12. Verify the scan tool ECM PNP Switch parameter is Park/Neutral.

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

7. If all circuits test normal, test or replace the PNP switch.

STRTR Relay Circuit Malfunction

1. Ignition OFF, disconnect the STRTR relay.
2. Ignition OFF and scan tool disconnected, open and close the driver door, and wait 1 minute. Test for less than 5 ohms between the ground circuit terminal 85 and ground.

⇒	If greater than the specified range, test the ground circuit for an open/high resistance.

3. Ignition ON, verify a test lamp illuminates between the B+ circuit terminal 30 and ground.

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

4. Ensure the parking brake is applied and the transmission is in PARK. Momentarily install a 40 A fused jumper wire between the B+ circuit terminal 30 and the control output circuit terminal 87. The starter solenoid should engage and the engine should begin cranking.

⇒	If the solenoid does not engage, test the control output circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the starter motor.

5. Connect a test lamp between the coil control circuit terminal 86 and the coil ground circuit terminal 85.
6. With the transmission in park, cycle the ignition switch between the OFF and START positions. The test lamp should turn ON and OFF when changing between the positions.

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

⇒	If the test lamp is always OFF, test the control 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 STRTR relay.

PNP Switch

1. Ignition OFF, disconnect the harness connector at the PNP switch.
2. With the PNP switch in the following positions, test for infinite resistance between the signal terminal 1 and the ignition terminal 12.

•

R

•

OD

•

D

•

2

•

1

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

3. With the PNP switch in the following positions, test for less than 2 ohms between the signal terminal 1 and the ignition terminal 12.

•

P

•

N

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

STRTR Relay

1. Ignition OFF, disconnect the STRTR relay.
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 20 amp 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 ohms between terminals 30 and 87.

⇒	If greater than specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.