The engine control module (ECM) provides 12 volts to the Park/Neutral switch circuit of the transmission internal mode switch (IMS). The IMS is a sliding contact assembly that attaches to the manual shaft inside of the transmission. The switch consists of five separate circuits, four of which indicate the gear selector position to the transmission control module (TCM), and one that indicates the Park/Neutral position to the ECM. When the transmission is in Park or Neutral, the switch closes and pulls the ECM voltage low on the signal circuit. When the transmission is not in Park or Neutral, the ECM voltage is high, near 12 volts. The ECM uses the switch in order to enable starter motor operation.

P0851

P0852

P0851

The Park/Neutral switch circuit voltage is low, 0 volts, for 0.01 seconds while the TCM is reporting the gear selector is in a reverse or drive gear.

P0852

The Park/Neutral switch circuit is high, 12 volts, for 0.01 seconds while the TCM is reporting the gear selector is in Park or Neutral.

P0851 and P0852 are Type C DTCs.

P0851 and P0852 are Type C DTCs.

The battery must be fully charged. Refer to Battery Inspection/Test.

Schematic Reference

Automatic Transmission Controls Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information.

1. Ignition ON, verify with a scan tool the PNP switch parameter displays Park/Neutral, when the gear shift lever is in the park or neutral position.
2. Ignition ON, verify with a scan tool the PNP switch parameter displays in gear when in reverse or any drive gear.
3. Perform the Range Selector Lever Cable Adjustment. Refer to Range Selector Lever Cable Adjustment.
4. Operate the vehicle within the conditions for running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records.

1. Ignition OFF, disconnect the X101 harness connector at the transmission.
2. Test for less than 5.0 ohms between the ground circuit terminal K and ground.

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

3. Ignition ON, verify with a scan tool the park/neutral switch parameter displays, in gear.

⇒	If not the specified value, test the signal circuit, terminal W for a short to ground. If the circuits test normal replace the control module.

4. Install a 3 A fused jumper wire between the signal circuit terminal W and the ground circuit terminal K. Verify the scan tool park/neutral switch parameter displays, park/neutral.

⇒	If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the powertrain control module (PCM).

5. Inspect the transmission internal wire harness circuits for opens, high resistance or shorts to grounds.

⇒	If a wire circuit condition is observed, replace the internal wire harness assembly.

6. If all circuits test normal, test or replace the IMS.

1. Ignition OFF, in Park, disconnect the X101 harness connector at the transmission.
2. Test for less than 5 ohms between terminal K and terminal W on the transmission side of connector X101.

⇒	If greater than the specified value, test the transmission internal wire harness for an open/high resistance. If the circuit tests normal replace the IMS.

3. Ignition OFF, in Reverse or Drive gear, test for greater than 5 ohms between terminal W and terminal K on the transmission side of X101.

⇒	If less than the specified value, test the transmission internal wire harness for a short to ground. If the circuit tests normal, replace the IMS.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.