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 low. This indicates to the ECM that conditions are acceptable for cranking. When a power mode crank request is seen, the ECM grounds the CRNK 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 X2 and 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 ECM Park Switch Circuit Malfunction.

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

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

ECM Park Switch Circuit Malfunction

1. Ignition OFF, disconnect the X175 AT inline 20-Way connector at the transmission.
2. Ignition OFF and scan tool disconnected, open and close the driver door, and wait 1 minute. Test for less than 5 Ω between the ground circuit terminal K and ground.

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

3. Ignition ON, verify the scan tool ECM PNP Switch parameter is In Gear.

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

4. Ignition ON, install a 3A fused jumper wire between the signal circuit terminal W and the ground circuit terminal K. Verify the scan tool ECM PNP switch parameter is Park/Neutral.

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

5. If all circuits test normal, test or replace the internal mode switch (IMS).

Starter Relay Circuit Malfunction

1. Ignition OFF, disconnect the CRNK relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 86 and ground.

⇒	If the test lamp illuminates, test the control circuit for a short to voltage.

3. Ignition ON, verify a test lamp illuminates between the ignition circuit terminal 85 and ground.

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

4. 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.

5. Apply the parking brake and shift the transmission into park. Connect a 40A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the starter solenoid engages and the engine cranks.

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

6. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
7. Transmission in park, turn the ignition switch between the OFF and CRANK 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 ground. If the circuit tests normal, replace the ECM.

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

8. If all circuits test normal, test or replace the CRNK relay.

Relay Test

1. Ignition OFF, disconnect the CRNK relay.
2. Test for 60-180 Ω 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 A fused jumper wire between relay terminal 85 and 12 V. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 Ω between terminals 30 and 87.

⇒	If greater than specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.