Subaru Legacy (2005 year). Manual - part 334

EN(H4DOTC)(diag)-105

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

R: DTC P0137 O2 SENSOR CIRCUIT LOW VOLTAGE (BANK 1 SENSOR 2)

DTC DETECTING CONDITION:
Detects when malfunction occurs in 2 continuous driving cycles.

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4DOTC)(diag)-
37, OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4DOTC)(diag)-30, PROCE-
DURE, Inspection Mode.>.
WIRING DIAGRAM:

EN-03555

1 2 3 4
5 6 7 8

B83

BATTERY

MAIN RELAY

B47

1

2

4

6

3

5

E

E

B21

E2

35

*

*

B83

3

4

1

2

5

6

B135

B47

B19

B136

1

4

2

3

T6

         REAR
OXYGEN SENSOR

B4

B1

B2

D25

D31

C35

ECM

B136

B137

C:

B135

B:

D:

1

2

3

4

B:

C:

B137

D:

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

33 34

29

32

30

31

35

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

29 30 31

32 33

34 35

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

B19

T5

2

T5

B19

3

1

4

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

T6

2 1
4 3

*

: TERMINAL No. RANDOM ARRANGEMENT

EN(H4DOTC)(diag)-106

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK ANY OTHER DTC ON DISPLAY.

Is any other DTC displayed?

Check DTC using 
“List of Diagnostic 
Trouble Code 
(DTC)”. <Ref. to 
EN(H4DOTC)(diag
)-62, List of Diag-
nostic Trouble 
Code (DTC).>

Go to step 2.

2

CHECK REAR OXYGEN SENSOR DATA.
1) Warm-up the engine until engine coolant 
temperature is above 70

°C (158°F), and keep 

the engine speed at 2,000 to 3,000 rpm for two 
minutes.
2) Read the data of rear oxygen sensor signal 
using Subaru Select Monitor or general scan 
tool.

NOTE:

• Subaru Select Monitor
For detailed operation procedure, refer to 
“READ CURRENT DATA FOR ENGINE”. <Ref. 
to EN(H4DOTC)(diag)-24, Subaru Select Mon-
itor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Does the value fluctuate?

Go to step 6.

Go to step 3.

3

CHECK REAR OXYGEN SENSOR DATA.
Read the data of rear oxygen sensor signal 
using Subaru Select Monitor.

Is the voltage 0.2 — 0.4 V?

Go to step 4.

Replace the rear 
oxygen sensor. 
<Ref. to 
FU(H4DOTC)-33, 
Rear Oxygen Sen-
sor.>

4

CHECK HARNESS BETWEEN ECM AND 
REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM and 
rear oxygen sensor.
3) Measure the resistance of harness 
between ECM and rear oxygen sensor con-
nector.

Connector & terminal

(B137) No. 25 — (T6) No. 4:

Is the resistance more than 3 
Ω?

Repair the open 
circuit of harness 
between ECM and 
rear oxygen sen-
sor connector.

Go to step 5.

5

CHECK HARNESS BETWEEN REAR OXY-
GEN SENSOR AND ECM CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from rear oxygen 
sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between rear oxygen 
sensor harness connector and chassis ground.

Connector & terminal

(T6) No. 4 (+) — Chassis ground (

−

):

Is the voltage more than 0.2 V? Replace the rear 

oxygen sensor. 
<Ref. to 
FU(H4DOTC)-33, 
Rear Oxygen Sen-
sor.>

Repair the har-
ness and connec-
tor.

NOTE:
In this case, repair
the following:
• Open circuit of 
harness between 
rear oxygen sen-
sor and ECM con-
nector
• Poor contact in 
rear oxygen sen-
sor connector
• Poor contact in 
ECM connector

EN(H4DOTC)(diag)-107

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

6

CHECK EXHAUST SYSTEM.
Check exhaust system parts.

NOTE:

Check the following items.
• Loose part and incomplete installation of 
exhaust system
• Damage (crack, hole etc.) of parts
• Looseness and ill fitting of parts between 
front oxygen (A/F) sensor and rear oxygen 
sensor

Is there any fault in exhaust 
system?

Repair or replace 
faulty parts.

Replace the rear 
oxygen sensor. 
<Ref. to 
FU(H4DOTC)-33, 
Rear Oxygen Sen-
sor.>

Step

Check

Yes

No

EN(H4DOTC)(diag)-108

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

S: DTC P0138 O2 SENSOR CIRCUIT HIGH VOLTAGE (BANK 1 SENSOR 2)

DTC DETECTING CONDITION:
Detects when malfunction occurs in 2 continuous driving cycles.

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4DOTC)(diag)-
37, OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4DOTC)(diag)-30, PROCE-
DURE, Inspection Mode.>.
WIRING DIAGRAM:

EN-03555

1 2 3 4
5 6 7 8

B83

BATTERY

MAIN RELAY

B47

1

2

4

6

3

5

E

E

B21

E2

35

*

*

B83

3

4

1

2

5

6

B135

B47

B19

B136

1

4

2

3

T6

         REAR
OXYGEN SENSOR

B4

B1

B2

D25

D31

C35

ECM

B136

B137

C:

B135

B:

D:

1

2

3

4

B:

C:

B137

D:

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

33 34

29

32

30

31

35

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

29 30 31

32 33

34 35

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

B19

T5

2

T5

B19

3

1

4

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

T6

2 1
4 3

*

: TERMINAL No. RANDOM ARRANGEMENT