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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

CAUTION:

After servicing or replacing faulty parts, perform Clear Memory Mode Ref. to ENGINE (DIAGNOSTICS) (H6DO)>CLEAR MEMORY MODE>OPERATION ., and inspection mode Ref. to ENGINE (DIAGNOSTICS) (H6DO)>INSPECTION MODE>PROCEDURE .
Use the check board when measuring the ECM terminal voltage and resistance.

Wiring diagram:

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

G12410258

Courtesy of SUBARU OF AMERICA, INC.

CHECK SELECT CABLE .
Check the select cable.

Is there any fault in select cable?

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

Yes:

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

(B134) No. 5 (+) - Chassis 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 .
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(TR690)>INHIBITOR SWITCH .

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