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) (H4DOTC)>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) (H4DOTC)>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 chassis ground.
  Connector & terminal
  
  (E158) No. 17 - 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 ECM connector and chassis ground.
  Connector & terminal
  
  (E158) No. 17 - Engine ground:
  
  Is the resistance 1 MΩ or more?
  
  Yes : Replace the inhibitor switch. Ref. to CONTINUOUSLY VARIABLE TRANSMISSION (TR690)>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