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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 .

G16446414

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
  
  (E159) No. 12 - 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
  
  (E159) No. 12 - 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