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Home >> Subaru >> 2019 >> WRX Base >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Control System (Diagnostics) (Except For STI) (3 Of 4) >> Diagnostic Procedure With Diagnostic Trouble Code (DTC) >> DTC P0851: Park/Neutral Switch Input Circuit LOW >> MT Model

MT Model

DTC detecting condition: 

Detected when two consecutive driving cycles with fault occur.

Trouble symptom: 

Improper idling

CAUTION:

Wiring diagram: 

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

G11577214Courtesy of SUBARU OF AMERICA, INC.
  1. CHECK INPUT SIGNAL OF ECM. 
    1. Turn the ignition switch to ON.
    2. Place the gear shift lever in a position other than neutral.
    3. Measure the voltage between ECM connector and engine ground.

      Connector & terminal 

      (B134) No. 33 (+) - Engine ground (-):

    Is the voltage 10 V or more?

    Yes:  Repair the poor contact of ECM connector.

    No:  Go to  2.

  2. CHECK HARNESS BETWEEN ECM AND NEUTRAL POSITION SWITCH CONNECTOR. 
    1. Turn the ignition switch to OFF.
    2. Disconnect the connector from ECM.
    3. Disconnect the connector from the neutral position switch.
    4. Measure the resistance between the ECM connector and engine ground.

      Connector & terminal 

      (B134) No. 33 - Engine ground:

    Is the resistance 1 MΩ or more?

    Yes:  Replace the neutral position switch. Refer to MANUAL TRANSMISSION AND DIFFERENTIAL (6MT) (TY75)>SWITCHES AND HARNESS .

    No:  Repair the short circuit to ground harness between ECM connector and neutral position switch connector.