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 automatic transmission is in Park / Neutral. If it is, the ECM then supplies 12 volts to the control circuit of the CRNK relay. When this occurs, battery voltage is supplied through the switch of the crank relay to 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

Automatic Transmission

1. Ignition ON, transmission in Park or Neutral, verify the scan tool ECM PNP Switch parameter reads Park/Neutral.

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

2. Command the Starter Relay ON with a scan tool. The starter solenoid should engage and the engine should crank.

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

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

IMS Switch Circuit Malfunction

1. Ignition OFF, disconnect the harness connector at the AT Inline 20-Way Connector.
2. Ignition ON, verify the scan tool PNP Switch parameter displays In Gear.

⇒	If not the specified value, test the signal circuit terminal  2 for a short to ground. If the circuit tests normal, replace the ECM.

3. Install a 3A fused jumper wire between the ignition circuit terminal  2 and ground. Verify the scan tool PNP Switch parameter reads 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.

4. If all circuits test normal, test or replace the IMS switch.

Crank Relay Circuit Malfunction

1. Ignition OFF, disconnect the crank relay.
2. Ignition OFF, Ignition OFF, test for less than 5.0  ohms between the relay 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 relay switch 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 40A 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 range selector in park or neutral, cycle the ignition key between the OFF and CRANK position. 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.

7. If all circuits test normal, test or replace the crank relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.