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 .

Courtesy of SUBARU OF AMERICA, INC.

CAUTION: Use the check board when measuring the ECM terminal voltage and resistance. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>GENERAL DESCRIPTION>PREPARATION TOOL>HOW TO USE CHECK BOARD .

NOTE: After the faulty parts are repaired or replaced, perform the final check in Basic Diagnostic Procedure. Ref. to ENGINE (DIAGNOSTICS) (H4DO)>BASIC DIAGNOSTIC PROCEDURE>PROCEDURE .

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 .
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 engine ground.
  Connector & terminal
  
  (B134) No. 39 (+) - Engine ground (-):
  
  Is the voltage 10 V or more?
  
  Yes
  
  Repair the poor contact of ECM connector.
  
  No
  
  Go to 3 .
CHECK HARNESS BETWEEN ECM AND TRANSMISSION HARNESS CONNECTOR (SHORT TO GROUND) .
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 the ECM connector and engine ground.
  Connector & terminal
  
  (B134) No. 39 - Engine ground:
  
  Is the resistance 1 MΩ or more?
  
  Yes
  
  Replace the inhibitor switch. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION(TR580)>INHIBITOR SWITCH .
  
  No
  
  Repair the following item.
  - Short circuit to ground in harness between ECM connector and inhibitor switch connector
  - Poor contact of coupling connector