Transmission Control Module (TCM) - 8HP45

P0850-PARK/NEUTRAL SWITCH PERFORMANCE

For a complete wiring diagram Refer to the Wiring Information.

Theory of Operation

The purpose of the diagnostic is to monitor the rationality of the park pawl sensor signal. The sensor has two pins to determine the position of the park pawl and two types of faults are monitored: If the output of the sensor is undefined or the sensor is too long in the intermediate position, DTC P0850 will set.

- When Monitored:
After the ignition switch is turned to the run position, no failures detected in the sensor supply voltage and no failures detected in electrical monitoring of the park pawl sensor.

- Set Condition:
The failure is detected if one of the following failure modes occurs: An undefined output signal of the park pawl sensor or the sensor signal is in the intermediate position for longer than a calibrated amount of time.





Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. 8HP45 Pre-Diagnostic Troubleshooting Procedure

1. CHECK IF DTC IS CURRENT

NOTE: The Transmission Control Module stores under Environmental Data the transmission operating conditions when the DTC was set. Before clearing any DTCs, record all information pertaining to the DTC.

1. With the scan tool, CLEAR transmission DTCs.
2. Using the Environmental Data previously recorded and try to duplicate the condition in which the DTC set.

Does the DTC reset?

Yes

- Go To 2

No

- Go To 3

2. TRANSMISSION CONTROL MODULE ASSEMBLY (TCMA)

If there are no possible causes remaining, view repair.

Repair

- Using the schematics as a guide, check the TCMA terminals for corrosion, damage or terminal push out. Pay particular attention to power and ground circuits. Check Service Information Tune-ups or Service Bulletins for possible causes that may apply. Remove the transmission oil pan and the TCMA. Valve Body - Removal. Inspect and clean the Park Pawl sensor terminals at the wiring harness leadframe for metallic contamination. Reinstall the TCMA. Valve Body - Installation. Connect the scan tool and clear the DTCs. Road test the vehicle and check for DTCs. If the DTC returns, replace and program the TCMA. Valve Body - Removal.
- Perform the TRANSMISSION VERIFICATION TEST. Verification Tests.

3. INTERMITTENT WIRING AND CONNECTORS
1. The conditions necessary to set this DTC are not present at this time.
2. Using the schematics as a guide, inspect the wiring and connectors specific to this circuit.
3. Wiggle the wiring and connectors while checking for any possible open or shorted circuits.
4. Check for any Service Information Tune-ups or Technical Service Bulletins that may apply.

Were any problems found?

Yes

- Repair as necessary.
- Perform the TRANSMISSION VERIFICATION TEST. Verification Tests.

No

- Test Complete.