DTC P0851 - Neutral Switch Input Circuit Low (Mt Model) -

WARNING: This page is about a different variant/trim than selected.

DTC DETECTING CONDITION:
- Two consecutive driving cycles with malfunction
TROUBLE SYMPTOM:
- Erroneous idling
CAUTION: After repair or replacement of malfunctioning parts, conduct Clear Memory Mode < Ref. to OPERATION , CLEAR MEMORY MODE > and INSPECTION MODE < Ref. to OPERATION , INSPECTION MODE. >
WIRING DIAGRAM:

Fig 1: Neutral Switch Input Wiring Diagram
Courtesy of SUBARU OF AMERICA, INC.

DIAGNOSTIC PROCEDURE

Step	Check	Yes	No
1 CHECK INPUT SIGNAL FOR ECM. Turn ignition switch to ON. Place the shift lever in neutral position. Measure voltage between ECM and chassis ground. Connector & terminal (B136) No. 21 (+) - Chassis ground (-):	Is the measured value less than 1 V?	Go to step 2.	Go to step 4.
2 CHECK INPUT SIGNAL FOR ECM. Place the shift lever in any other than neutral position. Measure voltage between ECM and chassis ground. Connector & terminal (B136) No. 21 (+) - Chassis ground (-):	Is the measured value more than 5 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 with SOA service center. NOTE: Inspection by DTM is required, because probable cause is deterioration of multiple parts.
4 CHECK NEUTRAL POSITION SWITCH. Turn ignition switch to OFF. Disconnect connector from transmission harness. Place the shift lever in neutral position. Measure resistance between transmission harness and connector terminals. Connector & terminal (T2) No. 1 - No. 2:	Is the measured value 1 MΩ or less?	Go to step 5.	Repair open circuit in transmission harness or replace neutral position switch.
5 CHECK HARNESS BETWEEN ECM AND NEUTRAL POSITION SWITCH CONNECTOR. Disconnect connector from ECM. Measure resistance between ECM and chassis ground. Connector & terminal (B136) No. 21 - Chassis ground:	Is the measured value more than 1 MΩ?	Go to step 6.	Repair ground short circuit in harness between ECM and transmission harness connector.
6 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 with SOA service center. NOTE: Inspection by DTM is required, because probable cause is deterioration of multiple parts.