Subaru Legacy III (2000-2003 year). Manual — part 226

EN(H4SOw/oOBD)-94

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. 12 (+) — Chassis ground (–):

Is the measured value within the specified
value?

0.5 — 4.5 V

Go to step 3.

Go to step 2.

2

CHECK POOR CONTACT.
Is there poor contact in ECM connector?

There is poor contact.

Repair poor con-
tact in ECM con-
nector.

Replace ECM.
<Ref. to
FU(H4SOw/
oOBD)-42, Engine
Control Module.>

3

CHECK HARNESS BETWEEN CO RESIS-
TOR AND ECM CONNECTOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from ECM and CO

resistor.

3) Measure resistance of harness between

ECM and CO resistor connector.

Connector & terminal

(B136) No. 15 — (B155) No. 1:
(B136) No. 12 — (B155) No. 2:
(B136) No. 16 — (B155) No. 3:

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

1

Ω

Go to step 4.

Repair open circuit
in harness
between ECM and
CO resistor con-
nector.

4

CHECK HARNESS BETWEEN CO RESIS-
TOR AND ECM CONNECTOR.
Measure resistance of harness between ECM
connector and chassis ground.

Connector & terminal

(B136) No. 15 — Chassis ground:
(B136) No. 12 — Chassis ground:
(B136) No. 16 — Chassis ground:

Does the measured value exceed the specified
value?

1 M

Ω

Go to step 5.

Repair short circuit
in harness
between ECM and
CO resistor con-
nector.

5

CHECK CO RESISTOR.
Measure resistance between CO resistor ter-
minals.

Terminals

No. 1 — No. 3:

Is the measured value within the specified
value?

4 — 6 k

Ω

Go to step 6.

Replace CO resis-
tor.

6

CHECK CO RESISTOR.
Measure variable resistance between CO
resistor terminals while rotating the screw of
CO resistor.

Terminals

No. 1 — No. 2:

Is the measured value within the specified
value?

0 — 6 k

Ω

Replace ECM.

Replace CO resis-
tor.

NOTE:
Ensure resistance
varies in response
to screw rotation.

EN(H4SOw/oOBD)-95

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

O: DTC 51 NEUTRAL POSITION SWITCH (MT VEHICLE)

• DIAGNOSIS:

• The neutral position switch signal is abnormal.
• The harness connector between ECM and neutral position switch is in short or open.

• TROUBLE SYMPTOM:

• Erroneous idling

CAUTION:
After repair or replacement of faulty parts, conduct CLEAR MEMORY and INSPECTION MODES. <Ref.
to EN(H4SOw/oOBD)-28, OPERATION, Clear Memory Mode.> and <Ref. to EN(H4SOw/oOBD)-26, OP-
ERATION, Inspection Mode.>
• WIRING DIAGRAM:

EN-01062

26

2

1

B25

T2

E3

B22

5 6 7

8

2

1

9

4

3

10

24

22 23

25

11 12 13 14 15

26

27 28

16 17 18 19

20 21

B135

B25

1 2

B22

16

B135

ECM

NEUTRAL

POSITION SWITCH

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

EN(H4SOw/oOBD)-96

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK INPUT SIGNAL FOR ECM.
1) Select MT shift lever to neutral position.
2) Turn ignition switch to ON.
3) Measure voltage between ECM and chas-

sis ground.

Connector & terminal

(B135) No. 26 (+) — Chassis ground (

−−−−

):

Is the measured value within the specified
value?

4.5 — 5.5 V

Go to step 3.

Go to step 2.

2

CHECK INPUT SIGNAL FOR ECM.
1) Select MT shift lever in any position other

than neutral.

2) Measure voltage between ECM and chas-

sis ground.

Connector & terminal

(B135) No. 26 (+) — Chassis ground (

−−−−

):

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

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.

Replace ECM.
<Ref. to
FU(H4SOw/
oOBD)-42, Engine
Control Module.>

4

CHECK NEUTRAL POSITION SWITCH.
1) Turn ignition switch to OFF.
2) Select MT shift lever to neutral position.
3) Disconnect connector from transmission

harness.

4) Measure resistance between transmission

harness and connector terminals.

Connector & terminal

(T2) No. 1 — No. 2:

Does the measured value exceed the spec-
ified value?

1 M

Ω

Go to step 5.

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

5

CHECK NEUTRAL POSITION SWITCH.
1) Move MT shift lever to any position other

than neutral.

2) Measure resistance between transmission

harness connector terminals.

Connector & terminal

(T2) No. 1 — No. 2:

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

10

Ω

Go to step 6.

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

6

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

ECM and transmission harness connector.

Connector & terminal

(B135) No. 26 — (B25) No. 1:

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

1

Ω

Go to step 7.

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

EN(H4SOw/oOBD)-97

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

7

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

Connector & terminal

(B135) No. 26 — Chassis ground:

Is the measured value less than the specified
value?

10

Ω

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

Go to step 8.

8

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.

Replace ECM.
<Ref. to
FU(H4SOw/
oOBD)-42, Engine
Control Module.>

Step

Value

Yes

No