Subaru Legacy (2005 year). Manual - part 476

EN(H6DO)(diag)-217

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

CD:DTC P0851 PARK/NEUTRAL SWITCH INPUT CIRCUIT LOW

DTC DETECTING CONDITION:
Detects when malfunction occurs in 2 continuous driving cycles.
TROUBLE SYMPTOM:
Erroneous idling

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(H6DO)(diag)-41, 
OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H6DO)(diag)-34, PROCEDURE, 
Inspection Mode.>.
WIRING DIAGRAM:

EN-03505

1

B128

3

B137

9

B128

E2

1 2

B25

E

NEUTRAL 
POSITION 
SWITCH

ECM

B137

5

6

7

8

2

1

9

4

3

10

22 23

11 12 13 14 15

24 25

26

16 17

18 19 20 21

27

28 29

30 31

B21

B21

1 2 3 4

12 13 14 15

5 6 7 8

16 17 18 19

9 10 11

20 21 22

23 24 25 26 27 28 29 30 31 32 33

35

34

37

36

39

38

41

40

43

42

44

45

47

46

49

48

51

50

53

52

54

B138

B138

1 2 3 4
5 6 7 8

1 2
3 4

B128

LHD

LHD

RHD

RHD

*

*

*

36

 LHD : T2
 RHD : T9 

*

*

EN(H6DO)(diag)-218

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK INPUT SIGNAL OF ECM.
1) Turn the ignition switch to ON.
2) Place the shift lever in neutral.
3) 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 2.

Go to step 4.

2

CHECK INPUT SIGNAL OF ECM.
1) Place the shift lever except in neutral.
2) 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 3.

Go to step 4.

3

CHECK POOR CONTACT.
Check poor contact in ECM connector.

Is there poor contact in ECM 
connector?

Repair the poor 
contact in ECM 
connector.

Replace the ECM.

4

CHECK NEUTRAL POSITION SWITCH.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from transmis-
sion harness.
3) Place the shift lever in neutral.
4) Measure the resistance between transmis-
sion harness and connector terminals.

Connector & terminal

LHD model

(T2) No. 1 — No. 3:

RHD model

(T9) No. 1 — No. 3:

Is the resistance less than 1 
Ω?

Go to step 5.

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

5

CHECK NEUTRAL POSITION SWITCH.
1) Place the shift lever except in neutral.
2) Measure the resistance between transmis-
sion harness connector terminals.

Connector & terminal

LHD model

(T2) No. 1 — No. 3:

RHD model

(T9) No. 1 — No. 3:

Is the resistance more than 1 
M

Ω?

Go to step 6.

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

6

CHECK HARNESS BETWEEN ECM AND 
NEUTRAL POSITION SWITCH CONNEC-
TOR.
Measure the resistance between ECM and 
chassis ground.

Connector & terminal

(B137) No. 9 — Chassis ground:

Is the resistance more than 1 
M

Ω?

Go to step 7.

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

7

CHECK HARNESS BETWEEN ECM AND 
NEUTRAL POSITION SWITCH CONNEC-
TOR.
1) Disconnect the connector from ECM.
2) Measure the resistance of harness 
between ECM and transmission harness con-
nector.

Connector & terminal

(B137) No. 9 — (B128) No. 1:

Is the resistance less than 1 
Ω?

Go to step 8.

Repair the open 
circuit of harness 
between ECM and 
transmission har-
ness connector.

EN(H6DO)(diag)-219

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

8

CHECK HARNESS BETWEEN ECM AND 
NEUTRAL POSITION SWITCH CONNEC-
TOR.
Measure the resistance of harness between 
transmission harness connector and engine 
ground.

Connector & terminal

(B128) No. 3 — Engine ground:

Is the resistance less than 5 
Ω?

Go to step 9.

Repair the open 
circuit between 
transmission har-
ness connector 
and engine ground 
terminal.

9

CHECK POOR CONTACT.
Check poor contact in transmission harness 
connector.

Is there poor contact in trans-
mission harness connector?

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

Replace the ECM.

Step

Check

Yes

No

EN(H6DO)(diag)-220

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

CE:DTC P0852 PARK/NEUTRAL SWITCH INPUT CIRCUIT HIGH

DTC DETECTING CONDITION:
Detects when malfunction occurs in 2 continuous driving cycles.
TROUBLE SYMPTOM:
Erroneous idling

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(H6DO)(diag)-41, 
OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H6DO)(diag)-34, PROCEDURE, 
Inspection Mode.>.
WIRING DIAGRAM:

EN-03505

1

B128

3

B137

9

B128

E2

1 2

B25

E

NEUTRAL 
POSITION 
SWITCH

ECM

B137

5

6

7

8

2

1

9

4

3

10

22 23

11 12 13 14 15

24 25

26

16 17

18 19 20 21

27

28 29

30 31

B21

B21

1 2 3 4

12 13 14 15

5 6 7 8

16 17 18 19

9 10 11

20 21 22

23 24 25 26 27 28 29 30 31 32 33

35

34

37

36

39

38

41

40

43

42

44

45

47

46

49

48

51

50

53

52

54

B138

B138

1 2 3 4
5 6 7 8

1 2
3 4

B128

LHD

LHD

RHD

RHD

*

*

*

36

 LHD : T2
 RHD : T9 

*

*