P0851
DTC P0851 or P0852
Diagnostic Instructions
* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (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/System Description
The park/neutral position (PNP) switch is externally mounted on the transmission manual shaft. The switch consists of five separate circuits, four of which indicate gear selector position to the transmission control module (TCM), and one that indicates park/neutral position to the ECM. As the gear range selector lever is moved, the state of the P/N switch may change, causing the park/neutral signal circuit to open or close. An open circuit or switch indicates a drive range and a low voltage, 0 volts, signal at the engine control module (ECM). A closed circuit or switch indicates PARK or NEUTRAL and a high voltage, 12 volts, signal at the ECM. The ECM uses the PNP Switch status in order to enable starter operation.
Conditions for Running the DTC
* Ignition voltage is between 8-18 volts.
* The engine speed is 1,000 RPM or greater.
* The engine torque is at least 75 Nm (55 lb ft).
* The throttle position is 8 percent or greater.
* Vehicle speed is 10 km/h (6 mph) or greater.
Conditions for Setting the DTC
P0851
The ECM detects the Park/Neutral switch signal equals 12 volts, high, when the PNP switch reports a Park/Neutral range for 3 seconds.
P0852
The ECM detects the Park/Neutral switch signal equals 0 volts, low, when the PNP switch reports a Drive range for 3 seconds.
Action Taken When the DTC Sets
* DTCs P0851 and P0852 are Type C DTCs.
* The ECM uses PNP range for engine start-up.
Conditions for Clearing the DTC
DTCs P0851 and P0852 are Type C DTCs.
Diagnostic Aids
It is possible for this DTC to set due to a stack-up or misalignment issue, where no electrical fault is present. Ensure the gear shift selector cable is properly adjusted and there are no service bulletins that address this concern before replacing parts.
Reference Information
Schematic Reference
Automatic Transmission Controls Schematics (Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Electronic Component Description (Electronic Component Description)for park/neutral position switch information
Electrical Information Reference
* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing for Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference
Control Module References (Programming and Relearning)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 (Diagnostic Trouble Code (DTC) List - Vehicle).
2. Ignition ON, observe the scan tool ECM Park/Neutral 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 ECM Park/Neutral switch 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 Shift Control Cable Adjustment (4T45-E - Automatic Transmission).
4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.
Circuit/System Testing
1. Ignition OFF, disconnect the harness connector at the transmission range switch.
2. Ignition ON, verify the scan tool ECM Park/Neutral switch parameter displays In-Gear.
• If not the specified value, test the park/neutral signal circuit terminal 12 for a short to ground. If the circuit tests normal, replace the ECM.
3. Install a 3A fused jumper wire between the park/neutral signal circuit terminal 12 and ground. Verify the scan tool ECM Park/Neutral 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.
Component Testing
1. Ignition OFF, disconnect the AT harness connector at the transmission.
2. Using the terminal test kit, connect a test lamp between battery positive voltage and any of the TR signal circuits at the PNP switch. Referring to Transmission Range Switch Logic (Transmission Range Switch Logic) will ensure that the test lamp illuminates when the TR signal circuit that is being tested is grounded.
• If the test lamp does not illuminate when the circuit is grounded, replace the PNP switch.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the repair.
* Park/Neutral Position Switch Replacement (Service and Repair)
* Control Module References (Programming and Relearning)for ECM replacement, setup, and programming