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 (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: DTC P0851 Neutral Switch Input Circuit Low (MT Model)

Courtesy of SUBARU OF AMERICA, INC.

DTC P0851 NEUTRAL SWITCH INPUT CIRCUIT LOW (MT MODEL) DIAGNOSIS

Step	Check	Yes	No
1. CHECK INPUT SIGNAL FOR ECM. Turn the ignition switch to ON. Place the shift lever in 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 a position except for 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 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 neutral. Measure the resistance between transmission harness and connector terminals. Connector & terminal (12) No. 1 - No. 2:	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 a position except for neutral. Measure the resistance between transmission harness connector terminals. Connector & terminal (T2)No. 1-No. 2:	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 - (B25) 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 (B25) No. 2 - 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 SOA Service Center.