DTC P0851 Neutral Switch Input Circuit Low (Mt Model)

DTC DETECTING CONDITION:

Two consecutive driving cycles with fault
GENERAL DESCRIPTION < Ref. to DTC P0851 NEUTRAL SWITCH INPUT CIRCUIT LOW (AT MODEL) , Diagnostic Trouble Code (DTC) Detecting Criteria. > < Ref. to DTC P0851 NEUTRAL SWITCH INPUT CIRCUIT LOW (MT MODEL) , Diagnostic Trouble Code (DTC) Detecting Criteria. >

TROUBLE SYMPTOM:

Erroneous idling

CAUTION: After repair or replacement of faulty parts, conduct Clear Memory Mode < Ref. to , OPERATION , Clear Memory Mode. > and Inspection Mode < Ref. to , PROCEDURE , Inspection Mode. >.

WIRING DIAGRAM:

Fig 1: Wiring Diagram - Neutral Switch Input Circuit Low (MT MODEL)

Courtesy of SUBARU OF AMERICA, INC.

DTC P0851 DIAGNOSTIC PROCEDURE

Step	Check	Yes	No
1 CHECK INPUT SIGNAL FOR ECM. Turn the ignition switch to ON. Place the shift lever in a position except for neutral. Measure the voltage between ECM and chassis ground. Connector & terminal (B137) No. 9 (+) - Chassis ground (-):	Is the voltage more than 10 V?	Go to step 2.	Go to step 4.
2 CHECK INPUT SIGNAL FOR ECM. Place the shift lever in neutral. Measure the voltage between ECM and chassis ground. Connector & terminal (B137) No. 9 (+) - Chassis ground (-):	Is the voltage less than 1 V?	Go to step 3.	Go to step 4.
3 CHECK POOR CONTACT. Check poor contact in ECM connector.	Is there poor contact in ECM connector?	Repair poor contact in ECM connector.	Contact your SOA Service Center.
4 CHECK NEUTRAL POSITION SWITCH. Turn the ignition switch to OFF. Disconnect the connector from transmission harness. Place the shift lever in a position except for neutral. Measure the resistance between transmission harness and connector terminals. Connector & terminal (79) No. 1 - No. 3:	Is the resistance more than 1 MΩ?	Go to step 5.	Repair short circuit in transmission harness or replace neutral position switch.
5 CHECK NEUTRAL POSITION SWITCH. Place the shift lever in neutral. Measure the resistance between transmission harness connector terminals.	Is the resistance less than 1 Ω?	Go to step 6.	Repair short circuit in transmission harness or replace neutral position switch.
6 CHECK HARNESS BETWEEN ECM AND NEUTRAL POSITION SWITCH CONNECTOR. Measure the resistance between ECM and chassis ground. Connector & terminal (B137) No. 9 - Chassis ground:	Is the resistance more than 1 MΩ?	Go to step 7.	Repair ground short circuit in harness between ECM and transmission harness connector.
7 CHECK HARNESS BETWEEN ECM AND NEUTRAL POSITION SWITCH CONNECTOR. Disconnect the connector from ECM. Measure the resistance of harness between ECM and transmission harness connector. Connector & terminal (B137) No. 9 - (B128) No. 1:	Is the resistance less than 1 Ω?	Go to step 8.	Repair open circuit in harness between ECM and transmission harness connector.
8 CHECK HARNESS BETWEEN ECM AND NEUTRAL POSITION SWITCH CONNECTOR. Measure the resistance of harness between transmission harness connector and engine ground. Connector & terminal (B128) No. 1 - Engine ground:	Is the resistance less than 5 Ω?	Go to step 9.	Repair open circuit between transmission harness connector and engine ground terminal.
9 CHECK POOR CONTACT. Check poor contact in transmission harness connector.	Is there poor contact in transmission harness connector?	Repair poor contact in transmission harness connector.	Contact your SOA Service Center.