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 and engaging the starter solenoid.

A misadjusted range selector lever cable may result in a starter solenoid does not click condition.

Schematic Reference

Connector End View Reference

Master Electrical Component List

Description and Operation

Starting System Description and Operation

Electrical Information Reference

Scan Tool Reference

1. Ignition ON, verify that no starter relay, theft deterrent, or automatic transmission DTCs are set that would cause the ECM to disable starting.

⇒	If DTCs are set, refer to Diagnostic Trouble Code (DTC) List - Vehicle .

2. Ignition ON, observe the scan tool BCM Starter Switch parameter. Place ignition switch in the crank position, the parameter should display ON.

⇒	If not the specified value, refer to Power Mode Mismatch .

3. Transmission range selector in park , verify the scan tool ECM PNP Switch and TCM IMS parameters display Park/Neutral.

⇒	If the TCM IMS parameter does not indicate Park/Neutral, refer to Transmission Internal Mode Switch Logic .

⇒	If the ECM Park/Neutral parameter does not indicate Park/Neutral, refer to ECM Park Switch Circuit Malfunction.

4. Transmission range selector in park or neutral, 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 (4T65-E)

1. Ignition OFF, disconnect the harness connector at the AT inline 20-Way connector.
2. Ignition ON, install a 3A fused jumper wire between the signal circuit terminal W and ground. Verify the scan tool ECM PNP switch parameter displays Park/Neutral.

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

3. 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 a test lamp illuminates between the ignition circuit terminal 85 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, 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. Connect a test lamp between the control circuit terminal 86 and the ignition circuit terminal 85.
5. With the transmission range selector in park or neutral, cycle the ignition 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 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.

6. 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.

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

CRANK Relay

1. Ignition OFF, Remove the CRNK 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 CRNK relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.