Subaru Legacy IV (2008 year). Manual - part 548

EN(H6DO)(diag)-165

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

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

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H6DO)-63, DTC P0138 O2 SENSOR CIRCUIT HIGH VOLTAGE
(BANK 1 SENSOR 2), Diagnostic Trouble Code (DTC) Detecting Criteria.>

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H6DO)(diag)-52,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H6DO)(diag)-44, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:

B47

3

4

5

6

1

2

B22

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

1 2 3 4
5 6 7 8

B83

B138

3 4

1 2

E25

E61

B47

1

2

3

5

4

6

E3

B22

14

MAIN RELAY

2

4

3

1

E25

13

15

16

E3

B22

10

11

12

9

SBF-5

BATTERY

2

E61

4

3

1

*

1

*

1

*

1

B83

B138

ECM

B134

A:

B135

B:

B136

C:

B137

D3

A3

D2

D1

D7

A5

D:

C5

*

*

2

2

C4

E

B1

B15

B4

B30

35

34

52

36

37

B21

E2

E

E

 : TERMINAL No. OPTIONAL ARRANGEMENT

*

1

 : TERMINAL No. OPTIONAL ARRANGEMENT 
  AMONG 1, 2, 5 AND 6

*

2

EN-06868

16

10 11 12 13 14 15

25

24

30

9

8

7

17 18 19 20
28

21 22 23

29

32

31

1

2

3

4

5

6

27

26

33 34 35

B136

C:

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

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

29 30 31

32 33

34 35

B135

B:

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

B134

A:

B21

1 2 3 4 5 6 7 8 9 10 11

12 13 14 15 16 17 18 19 20 21 22
23 24 25 26 27 28 29 30 31 32 33

34

35

42

43

36

37

38

39

48

49

50

51

52

53

54

40

41

44

45

46

47

REAR
OXYGEN 
SENSOR LH

REAR
OXYGEN 
SENSOR RH

EN(H6DO)(diag)-166

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK REAR OXYGEN SENSOR DATA.
1) Warm up the engine until engine coolant 
temperature is above 75°C (167°F), and rapidly 
reduce the engine speed from 3,000 rpm.
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(H6DO)(diag)-34, Subaru Select Moni-
tor.>
• General Scan Tool
For detailed operation procedures, refer to the
general scan tool operation manual.

Is the voltage 250 mV or less?

Go to step 5.

Go to step 2.

2

CHECK REAR OXYGEN SENSOR CONNEC-
TOR AND COUPLING CONNECTOR.

Has water entered the connec-
tor?

Completely 
remove any water 
inside.

Go to step 3.

3

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

Connector & terminal

(B135) No. 4 — (E61) No. 3:
(B135) No. 30 — (E61) No. 4:

Is the resistance less than 1 

:? Go to step 4.

Repair the harness 
and connector.

NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM and rear oxy-
gen sensor con-
nector
• Poor contact of
coupling connector

4

CHECK HARNESS BETWEEN ECM AND 
REAR OXYGEN SENSOR.
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 connector and chassis ground.

Connector & terminal

(E61) No. 3 (+) — Chassis ground (–):

Is the voltage 0.2 — 0.5 V?

Replace the rear 
oxygen sensor. 
<Ref. to 
FU(H6DO)-34,
Rear Oxygen Sen-
sor.>

Repair the harness 
and connector.

NOTE:
In this case, repair
the following item:
• Open circuit of
harness between
the ECM and rear
oxygen sensor
• Poor contact of
the rear oxygen
sensor connector
• Poor contact in
ECM connector

5

CHECK EXHAUST SYSTEM.
Check exhaust system parts.

NOTE:
Check the following items.
• Looseness and improper attachment of ex-
haust system parts
• Damage (crack, hole etc.) of parts
• Looseness and improper attachment of parts
between front oxygen (A/F) sensor and rear ox-
ygen sensor

Is there any fault in exhaust 
system?

Repair or replace 
faulty parts.

Replace the rear 
oxygen sensor. 
<Ref. to 
FU(H6DO)-34, 
Rear Oxygen Sen-
sor.>

EN(H6DO)(diag)-167

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

AQ:DTC P0139 O2 SENSOR CIRCUIT SLOW RESPONSE (BANK 1 SENSOR 2)

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H6DO)-64, DTC P0139 O2 SENSOR CIRCUIT SLOW RE-
SPONSE (BANK 1 SENSOR 2), Diagnostic Trouble Code (DTC) Detecting Criteria.>

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H6DO)(diag)-52,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H6DO)(diag)-44, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:

B47

3

4

5

6

1

2

B22

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

1 2 3 4
5 6 7 8

B83

B138

3 4

1 2

E25

E61

B47

1

2

3

5

4

6

E3

B22

14

MAIN RELAY

2

4

3

1

E25

13

15

16

E3

B22

10

11

12

9

SBF-5

BATTERY

2

E61

4

3

1

*

1

*

1

*

1

B83

B138

ECM

B134

A:

B135

B:

B136

C:

B137

D3

A3

D2

D1

D7

A5

D:

C5

*

*

2

2

C4

E

B1

B15

B4

B30

35

34

52

36

37

B21

E2

E

E

 : TERMINAL No. OPTIONAL ARRANGEMENT

*

1

 : TERMINAL No. OPTIONAL ARRANGEMENT 
  AMONG 1, 2, 5 AND 6

*

2

EN-06868

16

10 11 12 13 14 15

25

24

30

9

8

7

17 18 19 20
28

21 22 23

29

32

31

1

2

3

4

5

6

27

26

33 34 35

B136

C:

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

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

29 30 31

32 33

34 35

B135

B:

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

B134

A:

B21

1 2 3 4 5 6 7 8 9 10 11

12 13 14 15 16 17 18 19 20 21 22
23 24 25 26 27 28 29 30 31 32 33

34

35

42

43

36

37

38

39

48

49

50

51

52

53

54

40

41

44

45

46

47

REAR
OXYGEN 
SENSOR LH

REAR
OXYGEN 
SENSOR RH

EN(H6DO)(diag)-168

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

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

Connector & terminal

(B135) No. 4 — (E61) No. 3:

Is the resistance less than 1 

:? Go to step 2.

Repair the harness 
and connector.

NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM and rear oxy-
gen sensor con-
nector
• Poor contact of
coupling connector

2

CHECK HARNESS BETWEEN ECM AND 
REAR OXYGEN SENSOR CONNECTOR.
Measure the resistance between rear oxygen 
sensor connector and chassis ground.

Connector & terminal

(E61) No. 3 — Chassis ground

Is the resistance 1 M

: or 

more?

Go to step 3.

Repair the ground 
short circuit of har-
ness between 
ECM and rear oxy-
gen sensor con-
nector.

3

CHECK REAR OXYGEN SENSOR.
Measure the resistance between rear oxygen 
sensor terminals.

Terminals

No. 3 — No. 4

Is the resistance less than 1 

:? Replace the rear 

oxygen sensor. 
<Ref. to 
FU(H6DO)-34,
Rear Oxygen Sen-
sor.>

Even if DTC is 
detected, the cir-
cuit has returned to 
a normal condition 
at this time. Repro-
duce the failure, 
and then perform 
the diagnosis 
again.

NOTE:
In this case, tem-
porary poor con-
tact of connector
may be the cause.