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

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; the circuit 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 high voltage and high voltage when the ECM expects low voltage.

Ignition voltage is between 8-18 volts.

DTC P0851

DTC P0852

The ECM detects the Park/Neutral switch signal equals 12 volts (In-Gear) when the IMS reports a Park/Neutral range for 0.2 seconds.

DTC P0851 and P0852 are Type C DTCs.

Schematic Reference

Connector End View Reference

DTC Type Reference

Electrical Information Reference

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 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 or Drive.
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 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 data.

1. Ignition OFF, disconnect the 20-way harness connector at the transmission.
2. Install the DT-47825-20 to the 20-way harness connector to the engine harness.
3. Test for less than 10 ohms between the adapter harness pin 18 and ground.

⇒	If greater than the specified range, test and repair the low reference circuit for an open/high resistance.

4. Ignition ON, verify that a test lamp illuminates between the adapter harness pins 18 and 20.

⇒	If the test lamp does not illuminate, test the park/neutral signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.

5. Ignition OFF, install the DT-47825-20 to the 20-way harness connector at the transmission.
6. Gear shift lever in Park, test for less than 1 ohm between the adapter harness pins 18 and 20.

⇒	If greater than the specified range, test the shaft position switch assembly, refer to Component Testing. If the shaft position switch assembly tests normal, replace the control solenoid (w/body and TCM) valve assembly.

7. Gear shift lever in D (drive), test for infinite resistance between the adapter harness pins 18 and 20.

⇒	If not the specified value, test the shaft position switch assembly, refer to Component Testing. If the switch assembly test normal, replace the control solenoid (w/body and TCM) valve assembly.

8. If all circuits test normal, replace the ECM.

1. Remove the control valve body cover, Refer to Control Valve Body Cover Replacement .
2. Disconnect the shaft position switch assembly harness connector.
3. Test for less than 1 ohm between the shaft position switch assembly harness connector pin F and the transmission case.

⇒	If greater than the specified range, replace the shaft position switch assembly.

4. Ignition ON, engine OFF, and the gear shift lever in reverse, test for infinite resistance between the shaft position switch assembly harness connector pin F and the transmission case.

⇒	If not the specified value, replace the shaft position switch assembly.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Important: