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 sends a serial data message to the engine control module (ECM) that crank has been requested. The ECM then verifies that the automatic transmission is in Park or Neutral, and that the immobilizer is not disabling engine starting. If conditions are acceptable for cranking, then the ECM supplies 12 V to the control circuit of the STRTR relay. When this occurs, battery voltage is supplied through the switch of the STRTR relay to terminal A X1 of the starter solenoid, and the engine cranks.

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, 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.

2. 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 STRTR 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. Ignition OFF, disconnect the harness connector at the PNP switch.
3. Ignition OFF and scan tool disconnected, open and close the driver door, and wait 30 seconds. Test for less than 5 Ω between the following switch ground circuit terminals and ground:

•	Terminal 1 X1 (ME7)

•	Terminal 11 X1 (MN5)

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

4. Ignition ON, switch disconnected, verify that the scan tool ECM PNP Switch parameter is In Gear.

⇒	If not the specified value, test the signal circuit terminal 7 X1 (MN5) or terminal 12 X1 (ME7) for a short to ground. If the circuit tests normal, replace the ECM.

5. Install a 3 A fused jumper wire between the ground circuit and the signal circuit. Verify that 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.

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

PNP Switch Circuit Malfunction - 6T70 (MH2/MH4)

1. Inspect the range selector lever cable for proper adjustment. Refer to Range Selector Lever Cable Adjustment.
2. Ignition OFF, disconnect the inline 20-way harness connector at the transmission.
3. Ignition ON, test for greater than 5 V on the park/neutral signal circuit terminal 20.

⇒	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 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, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM.

8. Connect a 3 A 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, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

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

STRTR Relay Circuit Malfunction

1. Ignition OFF, disconnect the STRTR relay.
2. Ignition OFF and scan tool disconnected, open and close the driver door, and wait 30 seconds. 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 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 STARTER fuse is open, test the starter control circuit terminal 87 for a short to ground.

4. Ignition OFF and transmission in park, connect a 30 A 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, cycle the ignition switch between OFF and START. 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 STRTR relay.

Relay Test

1. Ignition OFF, disconnect the STRTR relay.
2. Test for 60-180 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.