For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provides an overview of each diagnostic category.

### DTC Descriptor

DTC P0851: Park/Neutral Position (PNP) Switch Circuit Low Voltage
DTC P0852: Park/Neutral Position (PNP) Switch Circuit High Voltage

### Diagnostic Fault Information

Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
Park/Neutral Signal | P0851 | P0852 | P0852 | --

### Circuit/System Description

When the transmission is in Park or Neutral, the switch closes. The ECM uses the switch in order to enable starter operation.

### Conditions for Running the DTC

• | Ignition voltage is between 11-18 volts.

• | No VSS faults exist.

• | No communication faults between TCM and ECM.

### Conditions for Setting the DTC

#### P0851

The ECM detects the gear is in park or neutral while the following conditions are met:

• | Vehicle speed is greater than 10 km/h.

• | Torque command is greater than 60 Nm.

• | Effective pedal position is greater than 10 %.

• | Torque converter slip RPM is between -20 RPM and 20 RPM.

#### P0852

The ECM detects the gear is not in park or neutral while the gear position from TCM is park or neutral.

### Action Taken When the DTC Sets

DTCs P0851 and P0852 are Type C DTCs.

### Conditions for Clearing the DTC

DTCs P0851 and P0852 are Type C DTCs.

### Reference Information

#### Schematic Reference

Automatic Transmission Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Electronic Component Description

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Verification

1. If there are any other transmission related DTCs set, diagnose those DTCs first. Refer to Diagnostic Trouble Code (DTC) List - Vehicle.
2. Ignition ON, observe the scan tool ECM PNP switch parameter while moving the gear shift lever from Park, to Reverse and through all the ranges. The parameter should display Park/Neutral when in Park or Neutral and In-Gear when in Reverse, Drive, or Drive Low.
3. Observe the scan tool TCM Current Gear parameter while slowly moving the gear shift lever from Park, to Reverse and through all the ranges. Verify the gear position matches the scan tool parameter.

⇒ | If not the specified value, refer to Range Selector Lever Cable Adjustment.

### Circuit/System Testing

1. Ignition OFF, disconnect the harness connector at the transmission range switch.
2. Test for less than 10 Ω between the ground circuit terminal 6 and ground.

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

3. Ignition ON, verify the scan tool ECM PNP switch parameter displays In-Gear.

⇒ | If not the specified value, test the park/neutral signal circuit terminal 9 for a short to ground. If the circuit tests normal, replace the ECM.

4. Install a 3A fused jumper wire between the park/neutral signal circuit terminal 9 and ground. Verify the scan tool ECM PNP switch parameter displays Park/Neutral.

⇒ | If not the specified value, test the park/neutral signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

5. If all circuits test normal replace the park/neutral position switch.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• | Park/Neutral Position Switch Replacement

• | Control Module References for ECM replacement, setup, and programming