P0850

SYMPTOM
P0850-PARK/NEUTRAL SWITCH PERFORMANCE

WHEN MONITORED
Continuously with the transmission in Park, Neutral, or Drive and NOT in Limp-in mode.

SET CONDITION
This code will set if the PCM detects an incorrect Park/Neutral switch state for a given mode of vehicle operation. One trip fault. Three good trips to turn off the MIL.

POSSIBLE CAUSES
- TRS (T41) SENSE (P/N SENSE) CIRCUIT OPEN
- TRS (T41) SENSE (P/N SENSE) CIRCUIT SHORTED TO GROUND
- TRANSMISSION RANGE SENSOR
- PCM

Always perform the Pre-Diagnostic Troubleshooting procedure before proceeding. Scan Tool Testing and Procedures

DIAGNOSTIC TEST
1. P/N & D/R NOT IN CORRECT POSITION





Note: Check the TCM for DTCs, if P0706 is set in the TCM diagnose the TCM code before continuing.

Ignition on, engine not running.
With the scan tool, read the Park/Neutral Position Switch input state.
While moving the gear selector through all gear positions (Park to 1 and back to Park), monitor the scan tool display.
Did the scan tool display show P/N and D/R in the correct gear positions?
Yes>> Perform (NGC) POWERTRAIN VERIFICATION TEST VER-2. Powertrain Verification Test - Ver 2
No>> Go To 2

2. TRS (T41) SENSE (P/N SENSE) CIRCUIT OPEN





Turn the ignition off.
Disconnect the PCM harness connectors.
Disconnect the Transmission Range Sensor harness connector.

CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool # 8815 to perform diagnosis.

Measure the resistance of the TRS (T41) Sense (P/N Sense) circuit from the TRS harness connector to the appropriate terminal of special tool # 8815.
Is the resistance below 5.0 ohms?
Yes>> Go To 3
No>> Repair the open in the TRS (T41) Sense (P/N Sense) circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-2.

3. TRS (T41) SIGNAL CIRCUIT SHORTED TO GROUND





Measure the resistance between ground and the TRS (T41) Sense (P/N Sense) circuit at the TRS harness connector.
Is the resistance above 100k ohms?
Yes>> Go To 4
No>> Repair the short to ground in the TRS (T41) Sense (P/N Sense) circuit. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-2.

4. TRANSMISSION RANGE SENSOR





Measure the resistance between ground and the (T41) TRS Sense (P/N Sense) circuit while moving the gear selector through each gear in the TRS connector.

Note: The circuit is grounded in Park and Neutral and open in the other positions.

Did the resistance change from above 100 k ohms (open) to below 10.0 ohms (grounded)?
Yes>> Go To 5
No>> Replace the Transmission Range Sensor. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-2.

5. PCM

Note: Before continuing, check the PCM harness connector terminals for corrosion, damage, or terminal push out. Repair as necessary.

Using the schematics as a guide, inspect the wire harness and connectors. Pay particular attention to all Power and Ground circuits.
Were there any problems found?
Yes>> Repair as necessary. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-2.
No>> Replace and program the Powertrain Control Module per Service Information. Perform (NGC) POWERTRAIN VERIFICATION TEST VER-2.