DTC P0851: Park/Neutral Switch Input Circuit Low: Notes

DTC detecting condition: 

Detected when two consecutive driving cycles with fault occur.

Trouble symptom: 

Improper idling

Wiring diagram: 

Engine Electrical System Ref. to WIRING SYSTEM>ENGINE ELECTRICAL SYSTEM>WIRING DIAGRAM .

Courtesy of SUBARU OF AMERICA, INC.

1. CHECK SELECT CABLE  .

   Check the select cable.

   Is there any fault in select cable?

   Yes: Repair or adjust the select cable. Ref. to CONTROL SYSTEMS>SELECT CABLE .

   No: Go to  2 .

2. CHECK INPUT SIGNAL OF ECM  .
   1. Turn the ignition switch to ON.
   2. Place the select lever in other than "P" range and "N" range.
   3. Measure the voltage between ECM connector and chassis ground.

      Connector & terminal 

      (B134) No. 5 (+) - Chassis ground (-):

   Is the voltage 10 V or more?

   Yes: Repair the poor contact of ECM connector.

   No: Go to  3 .

3. CHECK HARNESS BETWEEN ECM AND TRANSMISSION HARNESS CONNECTOR  .
   1. Turn the ignition switch to OFF.
   2. Disconnect the connector from ECM.
   3. Disconnect the connector from inhibitor switch.
   4. Measure the resistance between ECM connector and chassis ground.

      Connector & terminal 

      (B134) No. 5 - Chassis ground:

   Is the resistance 1 MΩ or more?

   Yes: Replace the inhibitor switch. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION(TR580)>INHIBITOR SWITCH .

   No: Repair the short circuit to ground in harness between ECM connector and inhibitor switch connector.