P0850

P0850-PARK/NEUTRAL SWITCH PERFORMANCE

For a complete wiring diagram, refer to the Wiring Information.

Theory of Operation

The Park Neutral switch rationality test is enabled only for vehicles equipped with an automatic transmission. This diagnostic checks if the park/neutral switch is incorrectly stuck in the neutral position during driving conditions by comparing Vehicle Speed, Engine Speed, Throttle Position and Pressure Ratio to the fail thresholds and by looking at the state of the Park/Neutral Switch. The stuck in drive condition is not explicitly checked as the starter relay does not energize and therefore render the vehicle inoperable.

- 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. Two trip fault. Three good trips to turn off the MIL.





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

Diagnostic Test

1. ACTIVE DTC

NOTE: Check the Radio Frequency Hub Module (RFHM) and Shift Lever Assembly for DTCs. Diagnose any codes before continuing.

1. Ignition on, engine not running.
2. Using a scan tool, select View DTCs.

Is the DTC Active at this time?

Yes

- Go To 2

No

- Perform the INTERMITTENT CONDITION diagnostic procedure. Intermittent Condition Test.

2. CHECK THE (T120) PARK/NEUTRAL SIGNAL CIRCUIT FOR AN OPEN
1. Turn the ignition off.
2. Disconnect the PCM C1 harness connector.
3. Disconnect the RFHM harness connector.
4. Measure the resistance of the (T120) Park Neutral Signal circuit from the RFHM harness connector to the appropriate terminal of the PCM harness connector.

Is the resistance below 5.0 Ohms?

Yes

- Go To 3

No

- Repair the open in the (T120) Park/Neutral Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

3. CHECK THE (T120) PARK/NEUTRAL SIGNAL CIRCUIT FOR A SHORT TO GROUND
1. Measure the resistance between ground and the (T120) Park/Neutral Signal circuit at the PCM C1 harness connector.

Is the resistance above 100k Ohms?

Yes

- Go To 4

No

- Repair the short to ground in the (T120) Park/Neutral Signal circuit.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

4. CHECK THE (T120) PARK/NEUTRAL SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE AT THE PCM CONNECTOR
1. Turn the ignition off.
2. Measure the resistance between the (T120) Park/Neutral Signal circuit and all other circuits at the PCM C1 harness connector.

Is the resistance above 10k Ohms between the (T120) Park/Neutral Signal circuit and all other circuits?

Yes

- Go To 5

No

- Repair the (T120) Park/Neutral Signal circuit for a short to the circuit that measured below 10k Ohms.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

5. CHECK THE (T120) PARK/NEUTRAL SIGNAL CIRCUIT FOR A SHORT TO VOLTAGE AT THE RFHM CONNECTOR
1. Turn the ignition off.
2. Measure the resistance between the (T120) Park/Neutral Signal circuit and all other circuits at the RFHM harness connector.

Is the resistance above 10k Ohms between the (T120) Park/Neutral Signal circuit and all other circuits?

Yes

- Go To 6

No

- Repair the (T120) Park/Neutral Signal circuit for a short to the circuit that measured below 10k Ohms.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

6. POWERTRAIN CONTROL MODULE (PCM)
1. Using the wiring diagram/schematic as a guide, inspect the wiring and connectors between the Radio Frequency Hub Module (RFHM) and the Powertrain Control Module (PCM).
2. Look for any chafed, pierced, pinched or partially broken wires.
3. Look for broken, bent, pushed out or corroded terminals. Verify that there is good pin to terminal contact in the TRS and Powertrain Control Module connectors.
4. Perform any Technical Service Bulletins that may apply.

Were there any problems found?

Yes

- Repair as necessary.
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.

No

- Replace and program the Powertrain Control Module. .
- Perform the POWERTRAIN VERIFICATION TEST. Powertrain Verification Test.