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 P0850: Park/Neutral Position (PNP) Switch Circuit

### Circuit/System Description

The engine control module (ECM) provides 12 volts to the park/neutral switch of the manual shift shaft position switch. The manual shift shaft position switch is a sliding contact assembly that attaches to the manual shift shaft inside the transmission. 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. When the transmission is in PARK or NEUTRAL, the switch closes and pulls the ECM voltage low, 0 volts. When the transmission is not in PARK or NEUTRAL, the ECM voltage is high, 12 volts. The ECM uses the switch in order to enable starter operation.

### Conditions for Running the DTC

The ignition is ON.

### Conditions for Setting the DTC

DTC P0850 sets when either of the following conditions are true:

#### Condition 1

The park/neutral switch circuit is low, 0 volts, for 100 seconds while the TCM is reporting the gear selector is in REVERSE or any forward range.

#### Condition 2

The park/neutral switch circuit is high, 12 volts, for 200 seconds while the TCM is reporting the gear selector is in PARK or NEUTRAL.

### Action Taken When the DTC Sets

• | DTC P0850 is a Type C DTC.

• | The ECM uses the transmission range data to enable engine cranking.

### Conditions for Clearing the DTC

DTC P0850 is a Type C DTC.

### Reference Information

#### Schematic Reference

Automatic Transmission Controls Schematics

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Transmission General 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

Transmission Control Module Scan Tool Information

#### Special Tools

J 45681 Jumper Harness

### 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 20-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 20-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 20-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.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Refer to Control Module References for replacement, setup, and programming.

• | Manual Shift Shaft Position Switch Replacement

• | Transmission Internal Electrical Harness Replacement