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 or 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 (LAT, LY7, LZ4), IGN 1 fuse (LE5), 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. The parameter should be Park/Neutral.

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

4. 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 30 seconds. Test for less than 5 ohms between the ground circuit terminal 1 and ground.

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

5. Verify that 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 for 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 - 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 5 volts on the park/neutral signal circuit terminal 20.

⇒	If less than the specified range, 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 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 at the control solenoid valve assembly and ground. The scan tool ECM PNP Switch parameter should be Park/Neutral.

⇒	If not the specified value, replace the ECM.

9. If all components 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 30 seconds. Test for less than 5 ohms 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 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. If the circuit tests normal and the STRTR fuse is open, test the starter control circuit terminal 87 for a short to ground.

4. Ignition OFF and transmission in PARK, connect a 30A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. The engine should begin cranking.

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

5. Connect a test lamp between the ground circuit terminal 85 and the control circuit terminal 86.
6. Ignition ON and transmission in Park, command the START relay ON and OFF with a scan tool (LAT, LE5, LZ4), or cycle the ignition switch between OFF and START (LY7). The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay control circuit terminal 86 for a short to voltage. If the circuit tests normal, replace the ECM.

⇒	If the test lamp is always OFF, test the relay control circuit terminal 86 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 START relay.

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.