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 applies voltage to the starter 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 X1 and engaging the starter solenoid.

Schematic Reference

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. Verify that no starter relay, immobilizer, or automatic transmission DTCs are set that would cause the ECM to disable starting.

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

2. Ignition ON, observe the scan tool ECM Ignition 1 Signal parameter with a scan tool. The reading should be greater than 10.0 Volts.

⇒	If less than the specified value, test the ECM IGN fuse, the RUN/CRNK relay, and the ignition voltage circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

3. Ignition ON, transmission in Park, observe the scan tool ECM PNP Switch parameter with a scan tool. The reading should be Park/Neutral.

⇒	If the scan tool PNP Switch parameter is not Park/Neutral, refer to PNP Switch Circuit Malfunction.

4. Command the Starter Relay ON with the scan tool, or turn the ignition switch to the START position. The starter solenoid should engage and the engine should crank.

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

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

PNP Switch Circuit Malfunction - 4T45-E (ME7/MN5)

1. Inspect the shift control cable for proper adjustment. Refer to Shift Control Cable Adjustment .
2. Inspect the PNP switch for proper adjustment. Refer to Park/Neutral Position Switch Replacement .
3. Ignition OFF. Disconnect the harness connector at the PNP switch.
4. Ignition OFF and scan tool disconnected, open and close the driver door, and wait 45 seconds. Test for less than 5 ohms between the switch ground circuit terminal 1 and ground.

⇒	If the test lamp does not illuminate, test the ground circuit terminal 1 for an open/high resistance.

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

⇒	If not the specified value, test the signal circuit terminal 12 for a short to ground. If the circuit tests normal, replace the ECM.

6. Install a 3A fused jumper wire between the ground circuit terminal 1 and the signal circuit terminal 12. Verify that the scan tool ECM PNP Switch parameter is Park/Neutral.

⇒	If not the specified value, test the signal circuit terminal 12 for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

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

PNP Switch Circuit Malfunction - 6T40/6T45 (MH8)

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 ON, test for greater than 10 volts on the park/neutral signal circuit terminal 3.

⇒	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.

4. Ignition OFF, remove the control valve body cover. Refer to Control Valve Body Cover Replacement .
5. Connect the transmission inline 20-way connector, with the cover removed.
6. Disconnect the shift position switch connector from the TCM. Refer to Control Solenoid Valve and Transmission Control Module Assembly Replacement .
7. Ignition ON, verify that the scan tool ECM PNP Switch parameter is In Gear.

⇒	If not the specified value, replace the ECM.

8. Connect a 3A fused jumper wire between the park/neutral signal terminal F of the TCM and ground. The scan tool PNP Switch parameter should be Park/Neutral when the terminal is connected to ground.

⇒	If not the specified value, replace the ECM.

9. If all circuits test normal, test or replace the shift position switch.

PNP Switch Circuit Malfunction - 6T70 (MH2)

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 ON, test for greater than 10 volts on the park/neutral signal circuit terminal 20.

⇒	If there is less than 10 volts on the park/neutral signal circuit, test the circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

4. Ignition OFF, remove the control valve body cover. Refer to Control Valve Body Cover Replacement .
5. Connect the transmission inline 20-way connector, with the cover removed.
6. Disconnect the internal mode switch connector at the control solenoid valve assembly.
7. Ignition ON, verify that the scan tool PNP Switch parameter is In Gear.

⇒	If not the specified value, replace the ECM.

8. Connect a 3A fused jumper wire between the park/neutral signal terminal F at the control solenoid valve assembly and ground. The scan tool PNP Switch parameter should be Park/Neutral when the terminal is connected to ground.

⇒	If not the specified value, replace the ECM.

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

Start Relay Circuit Malfunction

1. Ignition OFF, disconnect the START relay.
2. Ignition OFF and scan tool disconnected, open and close the driver door, and wait 45 seconds. Test for less than 5 ohms between the relay ground circuit terminal 85 and ground.

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

3. Verify that 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 relay coil ground circuit terminal 85 and the relay coil control circuit terminal 86.
5. Ignition ON, transmission in Park, turn the ignition switch between the start and run positions. The test lamp should turn ON and OFF when changing between the commanded states.

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

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

6. Connect the START relay.
7. Install a test lamp between the starter terminal A X1 and ground.

Important: The engine may begin to crank.

8. Ignition ON, transmission in Park, turn the ignition switch to the start position. The test lamp should illuminate.

⇒	If the test lamp does not illuminate, test the starter control circuit terminal 87 for an open/high resistance. If the circuit tests normal, test or replace the START relay.

9. If all circuits test normal, test or replace the starter.

PNP Switch (ME7/MN5)

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 ground terminal 1 and the signal 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 ground terminal 1 and the signal terminal 12.

•

P

•

N

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

START Relay

1. Ignition OFF, disconnect the START 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 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 ohms between terminals 30 and 87.

⇒	If greater than specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.