Subaru Legacy III (2000-2003 year). Manual - part 161

EN(H4SO)-256

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

BM: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(H4SO)-47, OPER-
ATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO)-40, OPERATION, Inspection 
Mode.> .
• WIRING DIAGRAM:

EN-01137

2

1

21

B136

ECM

NEUTRAL
POSITION
SWITCH

B25

T2

T2

B25

B22

E3

15

B25

1 2

B22

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

B136

5 6

7

2

1

9

8

4

3

23

21 22

24

10 11 12 13 14

25 26

15 16 17

18 19 20

EN(H4SO)-257

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

(B136) No. 21 (+) — 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

(B136) No. 21 (+) — 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

(T2) 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

(B136) No. 21 — 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.

EN(H4SO)-258

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

BN:DTC P0852 — NEUTRAL SWITCH INPUT CIRCUIT HIGH (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(H4SO)-47, OPER-
ATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO)-40, OPERATION, Inspection 
Mode.> .
• WIRING DIAGRAM:

EN-00740

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

21

B136

ECM

STARTER MOTOR

1 2 3 4
5 6 7 8
9 10 11 12

B136

5 6

7

2

1

9

8

4

3

23

21 22

24

10 11 12 13 14

25 26

15 16 17

18 19 20

EN(H4SO)-259

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(H4SO)-83, List 
of Diagnostic 
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 in select level “N” and “P” posi-
tions.

Connector & terminal

(B136) No. 21 (+) — Chassis ground

Is the measured value less than the speci-
fied value?

1 V

Go to step 3.

Go to step 5.

3

CHECK INPUT SIGNAL FOR ECM.
Measure voltage between ECM and chassis 
ground in select level “N” and “P” positions.

Connector & terminal

(B136) No. 21 (+) — Chassis ground

Is the measured value within the specified 
range?

4.5 - 5.5 V

Go to step 4.

Go to step 5.

4

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.

5

CHECK HARNESS BETWEEN ECM AND IN-
HIBITOR SWITCH CONNECTOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from ECM and inhibi-

tor switch.

3) Measure resistance of harness between 

ECM and inhibitor switch connector.

Connector & terminal

(B136) No. 21 — (T7) No. 12:

Is the measured value less than the speci-
fied value?

1 

Ω

Go to step 6.

Repair harness 
and connector.

NOTE:
In this case, repair
the following:
• Open circuit in 
harness between 
ECM and inhibitor 
switch connector
• Poor contact in 
coupling connector
• Poor contact in 
inhibitor switch 
connector
• Poor contact in 
ECM connector