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 Descriptors
DTC P0851: Park/Neutral Position (PNP) Switch Circuit Low VoltageDTC 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 | P0852 | P0851 | P0851 | -- |
Typical Scan Tool Data
Circuit | Short to Ground | Open/High Resistance | Short to Voltage |
|---|---|---|---|
Operating Conditions: Engine running, normal operating temperature Parameter Normal Range: 12 Volts = In-Gear, 0 Volts = Park/Neutral | |||
Park/Neutral Signal | Park/Neutral | In-Gear | In-Gear |
Circuit/System Description
The transmission manual shift shaft switch assembly, also known as the internal mode switch (IMS), is a sliding contact switch attached to the manual shift shaft inside the transmission case. The Park/Neutral position (PNP) switch is integrated into the IMS and connects to the transmission control module (TCM) lead-frame through a short wire harness. The 5 inputs to the TCM from the transmission manual shift shaft switch assembly indicate the transmission gear selector lever position. This information is used for engine start enable, engine controls, as well as determining the transmission shift patterns. The state of each input is available for display on the scan tool. The five input parameters represented are signal A, signal B, signal C, signal P (parity) and signal N (Park/Neutral start signal). Park/Neutral signal is sent from the Park/Neutral switch directly to the engine control module (ECM) and is used for engine start enable. The Park/Neutral signal circuit is not connected to the TCM internally; it uses the TCM as a pass-through connector only. The ECM Park/Neutral diagnostic monitors the Park/Neutral signal circuit to detect low voltage when the ECM expects to see high voltage and high voltage when the ECM expects to see low voltage.
Conditions for Running the DTC
| • | Ignition voltage is between 9-18 volts. |
| • | No TCM DTCs P0601, P0602, P0603, or P0604. |
| • | No IMS DTCs P1825 or P1915. |
| • | No Communication DTCs U0001, U0100, U0101, U2105, or U2106. |
P0851
| • | No TP DTCs P0121, P0122, or P0123. |
| • | No OSS DTCs P0722 or P0723. |
| • | No MAF DTCs P0101, P0102, or P0103. |
| • | No MAP DTCs P0106, P0107, or P0108. |
| • | Engine speed is greater than 400 RPM. |
Conditions for Setting the DTC
P0851
The ECM detects the Park/Neutral switch signal equals 12 volts (high) when the IMS reports a Park/Neutral range for 0.2 seconds.
P0852
The ECM detects the Park/Neutral switch signal equals 0 volts (low) when the IMS reports a Drive range for 0.2 seconds and the following conditions are present:
| • | TP is equal to or greater than 10 percent. |
| • | Engine torque is equal to or greater than 75 N·m (55 lb ft). |
| • | Vehicle speed is equal or greater than 10 km/h (6 mph). |
Action Taken When the DTC Sets
| • | DTCs P0851 and P0852 are Type C DTCs. |
| • | The ECM uses IMS range for engine start-up. |
Conditions for Clearing the DIC/DTC
DTCs P0851 and P0852 are Type C DTCs.
Reference Information
Schematic Reference
Connector End View Reference
DTC Type Reference
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
If there are any other engine or transmission related DTCs set, diagnose those DTCs first. With a scan tool observe the Park/Neutral switch parameter in the engine controls data list and move the gear shift lever from Park, to Reverse and through all the ranges and observe the parameter as you move the shift lever. The parameter should display Park/Neutral when in Park or Neutral and In-Gear when in Reverse, Drive or Drive Low. Close observation of the Park and Neutral to Drive transitional positions while moving the shift lever and observing for possible misalignment or slack in the shifter mechanism is especially important.
| ⇒ | If any concerns are found proceed to Testing. |
Circuit/System Testing
Disconnect the transmission 16-way connector and observe the Park/Neutral scan tool parameter in the engine controls data list. The parameter should display In-Gear.
| ⇒ | If the Park/Neutral parameter does not display In-Gear test the Park/Neutral signal circuit between the engine side of the transmission 16-way connector and the ECM connector for a short to ground. |
| ⇒ | If the Park/Neutral parameter displays In-Gear test the transmission IMS for a shorted P/N circuit to ground. Inspect the harness for damage or chaffing. |
| ⇒ | If the IMS was not shorted to ground, test the IMS Park/Neutral signal circuit form the IMS connector on the TCM side of the 16-way connector for an open or short to ground. |
| ⇒ | If no concerns are found, replace the ECM. Refer to Control Module References for replacement, setup, and programming. |
Component Testing
Perform the Control Solenoid Valve and Transmission Control Module Assembly Inspection .
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- ECM replacement. Refer to Control Module References for replacement, setup, and programming.
- IMS replacement. Refer to Manual Shift Shaft Position Switch Replacement .
- Perform the Service Fast Learn Adapts .
