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 then sends a message to the engine control module (ECM) that crank has been requested. The ECM then verifies that the transmission is in park or neutral. If it is, the ECM then supplies 12 V to the control circuit of the CRNK relay. When this occurs, battery voltage is supplied through the CRNK relay 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 PNP Switch parameter while shifting the transmission. The reading should change between Park/Neutral and In Gear.

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

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

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

ECM Park Switch Malfunction

1. Inspect the range selector lever cable for proper adjustment. Refer to Range Selector Lever Cable Adjustment.
2. Ignition OFF, disconnect the harness connector at the transmission inline 20-way connector.
3. 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 18 and ground.

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

4. Ignition ON, test for greater than 5 V between the signal circuit terminal 20 and ground.

⇒	If less than the specified range, test the signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

5. Ignition OFF, remove the control valve body cover. Refer to Control Valve Body Cover Replacement.
6. Connect the transmission inline 20-way connector. Disconnect the shift position switch from the TCM.
7. 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 A of the TCM and ground.

⇒	If greater than the specified range, replace the TCM.

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

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

9. Install a 3 A fused jumper wire between the signal circuit terminal F and ground. Verify the scan tool 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.

10. If all circuits test normal, test or replace the internal mode switch.

CRNK Relay Malfunction

1. Ignition OFF, disconnect the CRNK relay.
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 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. Ignition ON, verify a test lamp does not illuminate between the control circuit terminal 87 and ground.

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

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

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

6. Connect a test lamp between the control circuit terminal 86 and the ground circuit terminal 85.
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 commanded states.

⇒	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.

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

Shift Position Switch Test

1. Ignition OFF, disconnect the shift position switch harness at the TCM.
2. With the switch in the following positions, test for infinite resistance between the ground terminal A and the signal terminal F.

•

R

•

OD

•

D

•

2

•

1

⇒	If not the specified value, replace the shift position switch.

3. With the switch in the following positions, test for less than 2 Ω between the ground terminal A and the signal terminal F.

•

P

•

N

⇒	If greater than the specified range, replace the shift position switch.

Relay Test

1. Ignition OFF, disconnect the CRNK relay.
2. Test for 60-250 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.