Subaru Legacy III (2000-2003 year). Manual - part 500

EN(H4DOSTC)-170

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

AM:DTC P0851 — NEUTRAL SWITCH INPUT CIRCUIT LOW (AT MODEL) —

• DTC DETECTING CONDITION:

• Two consecutive driving cycles with fault

• TROUBLE SYMPTOM:

• Erroneous idling

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode<Ref. to EN(H4DOSTC)-35, 
OPERATION, Clear Memory Mode.>  and Inspection Mode <Ref. to EN(H4DOSTC)-33, OPERATION, 
Inspection Mode.> .
• WIRING DIAGRAM:

EN-01003

12

INHIBITOR SWITCH

7

P

R

N

D

3

2

1

12

11

T7

T3

B12

B14

B12

T7

1 2 3 4 5 6
7 8 9 10 11 12

8

B134

ECM

STARTER MOTOR

1 2 3 4
5 6 7 8
9 10 11 12

B134

1 2 3 4

10 11 12

19 20 21

13

5

6

14 15

7

8 9

16 17

18

22

EN(H4DOSTC)-171

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK ANY OTHER DTC ON DISPLAY.
Is any other DTC displayed?

DTC indicated.

Inspect the rele-
vant DTC using 
“List of Diagnos-
tics Trouble Code 
(DTC)”. <Ref. to 
EN(H4DOSTC)-
62, List of Diag-
nostic Trouble 
Code (DTC).>

Go to step 2.

2

CHECK INPUT SIGNAL FOR ECM.
1) Turn ignition switch to ON.
2) Measure voltage between ECM and chas-

sis ground.

Connector & terminal

(B134) No. 8 (+) — Chassis ground (

−−−−

):

Is the measured value within the specified 
value at except “N” and “P” position?

4.5 V —  5.5 V

Even if MI lights 
up, the circuit has 
returned to a nor-
mal condition at 
this time.

Go to step 3.

3

CHECK HARNESS BETWEEN ECM AND 
TRANSMISSION HARNESS CONNECTOR.
1) Turn ignition switch to OFF.
2) Disconnect connectors from ECM and 

transmission harness connector (T3).

3) Measure resistance of harness between 

ECM connector and chassis ground.

Connector & terminal

(B134) No. 8 — Chassis ground:

Does the measured value exceed the spec-
ified value?

1 M

Ω

Go to step 4.

Repair ground 
short circuit in har-
ness between 
ECM and trans-
mission harness 
connector.

4

CHECK TRANSMISSION HARNESS CON-
NECTOR.
1) Disconnect connector from inhibitor switch.
2) Measure resistance of harness between 

transmission harness connector and 
engine ground.

Connector & terminal

(T3) No. 12 — Engine ground:

Does the measured value exceed the spec-
ified value?

1 M

Ω

Go to step 5.

Repair ground 
short circuit in har-
ness between 
transmission har-
ness and inhibitor 
switch connector.

5

CHECK INHIBITOR SWITCH.
Measure resistance between inhibitor switch 
connector receptacle's terminals in select lever 
except for “N” position.

Terminals

No. 7 — No. 12:

Does the measured value exceed the specified 
value at except “N” and “P” positions?

1 M

Ω

Go to step 6.

Replace inhibitor 
switch.  <Ref. to 
AT-49, Inhibitor 
Switch.>

6

CHECK SELECTOR CABLE CONNECTION.
Is there any fault in selector cable connection 
to inhibitor switch?

There is a fault.

Repair selector 
cable connection.  
<Ref. to CS-12, 
Select Cable.>

Contact SUBARU 
distributor service.

NOTE:
Inspection by DTM
is required, be-
cause probable
cause is deteriora-
tion of multiple
parts.

EN(H4DOSTC)-172

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

AN:DTC P0851 — NEUTRAL SWITCH INPUT CIRCUIT LOW (MT MODEL) —

• DTC DETECTING CONDITION:

• Two consecutive driving cycles with fault

• TROUBLE SYMPTOM:

• Erroneous idling

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode<Ref. to EN(H4DOSTC)-35, 
OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4DOSTC)-33, OPERATION, In-
spection Mode.> .
• WIRING DIAGRAM:

EN-01004

2

1

8

B134

ECM

NEUTRAL
POSITION
SWITCH

B128

T9

T9

B128

B22

E3

16

B128

B22

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

B134

3 4

1 2

1 2 3 4

10 11 12

19 20 21

13

5

6

14 15

7

8 9

16 17

18

22

EN(H4DOSTC)-173

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK INPUT SIGNAL FOR ECM.
1) Turn ignition switch to ON.
2) Measure voltage between ECM and chas-

sis ground.

Connector & terminal

(B134) No. 8 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the spec-
ified value in neutral position?

5 V

Go to step 2.

Go to step 4.

2

CHECK INPUT SIGNAL FOR ECM.
Measure voltage between ECM and chassis 
ground.

Connector & terminal

(B134) No. 8 (+) — Chassis ground (

−−−−

):

Is the measured value less than the specified 
value at except neutral position?

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?

There is poor contact.

Repair poor con-
tact in ECM con-
nector.

Contact SUBARU 
distributor service.

NOTE:
Inspection by DTM
is required, be-
cause probable
cause is deteriora-
tion of multiple
parts.

4

CHECK NEUTRAL POSITION SWITCH.
1) Turn ignition switch to OFF.
2) Disconnect connector from transmission 

harness.

3) Measure resistance between transmission 

harness and connector terminals.

Connector & terminal

(T9) No. 1 — No. 2:

Does the measured value exceed the spec-
ified value in neutral position?

1 M

Ω

Go to step 5.

Repair short circuit 
in transmission 
harness or replace 
neutral position 
switch.

5

CHECK HARNESS BETWEEN ECM AND 
NEUTRAL POSITION SWITCH CONNEC-
TOR.
1) Disconnect connector from ECM.
2) Measure resistance between ECM and 

chassis ground.

Connector & terminal

(B134) No. 8 — Chassis ground:

Does the measured value exceed the spec-
ified value?

1 M

Ω

Repair ground 
short circuit in har-
ness between 
ECM and trans-
mission harness 
connector.

Go to step 6.

6

CHECK POOR CONTACT.
Check poor contact in transmission harness 
connector.
Is there poor contact in transmission harness 
connector?

There is poor contact.

Repair poor con-
tact in transmis-
sion harness 
connector.

Contact SUBARU 
distributor service.

NOTE:
Inspection by DTM
is required, be-
cause probable
cause is deteriora-
tion of multiple
parts.