Subaru Legacy IV (2008 year). Manual - part 328

EN(H4DOTC)(diag)-133

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Z: DTC P0131 O2 SENSOR CIRCUIT LOW VOLTAGE (BANK 1 SENSOR 1)

DTC DETECTING CONDITION:
• Immediately at fault recognition
• GENERAL DESCRIPTION <Ref. to GD(H4DOTC)-46, DTC P0131 O2 SENSOR CIRCUIT LOW VOLT-
AGE (BANK 1 SENSOR 1), Diagnostic Trouble Code (DTC) Detecting Criteria.>

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4DOTC)(diag)-
52, OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4DOTC)(diag)-43, PRO-
CEDURE, Inspection Mode.>.
WIRING DIAGRAM:

EN-05669

SBF-5

B47

B21

E2

B21

E2

1

2

4

6

3

5

E

E

C2

C3

B8

B9

B1

B134

4

3

2

1

E79

3 4

1 2

3

4

1

2

5

6

B21

B47

E79

B134

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

A:

B135

B:

B136

C:

B137

D:

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

A:

D2

A5

D3

E2

B21

E

35

34

40

D7

36

D1

37

B138

*

*

*

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:

B135

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

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

B:

D:

1 2 3 4
5 6 7 8

B138

42

26

43

15

MAIN RELAY

BATTERY

FRONT 
OXYGEN (A/F)  
SENSOR

ECM

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

EN(H4DOTC)(diag)-134

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK FRONT OXYGEN (A/F) SENSOR 
CONNECTOR AND COUPLING CONNEC-
TOR.

Has water entered the connec-
tor?

Completely 
remove any water 
inside.

Go to step 2.

2

CHECK HARNESS BETWEEN ECM AND 
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM and 
front oxygen (A/F) sensor connector.
3) Measure the resistance between ECM and 
chassis ground.

Connector & terminal

(B135) No. 9 — Chassis ground:
(B135) No. 8 — Chassis ground:

Is the resistance 1 M

: or 

more?

Go to step 3.

Repair the ground 
short circuit of har-
ness between 
ECM and front oxy-
gen (A/F) sensor 
connector.

3

CHECK POOR CONTACT.
Check for poor contact in the front oxygen (A/F) 
sensor connector.

Is there poor contact in front 
oxygen (A/F) sensor connec-
tor?

Repair the poor 
contact of the front 
oxygen (A/F) sen-
sor connector.

Replace the front 
oxygen (A/F) sen-
sor. <Ref. to 
FU(H4DOTC)-46, 
Front Oxygen (A/F) 
Sensor.>

EN(H4DOTC)(diag)-135

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

AA:DTC P0132 O2 SENSOR CIRCUIT HIGH VOLTAGE (BANK 1 SENSOR 1)

DTC DETECTING CONDITION:
• Immediately at fault recognition
• GENERAL DESCRIPTION <Ref. to GD(H4DOTC)-48, DTC P0132 O2 SENSOR CIRCUIT HIGH VOLT-
AGE (BANK 1 SENSOR 1), Diagnostic Trouble Code (DTC) Detecting Criteria.>

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4DOTC)(diag)-
52, OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4DOTC)(diag)-43, PRO-
CEDURE, Inspection Mode.>.
WIRING DIAGRAM:

EN-05669

SBF-5

B47

B21

E2

B21

E2

1

2

4

6

3

5

E

E

C2

C3

B8

B9

B1

B134

4

3

2

1

E79

3 4

1 2

3

4

1

2

5

6

B21

B47

E79

B134

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

A:

B135

B:

B136

C:

B137

D:

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

A:

D2

A5

D3

E2

B21

E

35

34

40

D7

36

D1

37

B138

*

*

*

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:

B135

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

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

B:

D:

1 2 3 4
5 6 7 8

B138

42

26

43

15

MAIN RELAY

BATTERY

FRONT 
OXYGEN (A/F)  
SENSOR

ECM

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

EN(H4DOTC)(diag)-136

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK FRONT OXYGEN (A/F) SENSOR 
CONNECTOR AND COUPLING CONNEC-
TOR.

Has water entered the connec-
tor?

Completely 
remove any water 
inside.

Go to step 2.

2

CHECK HARNESS BETWEEN ECM AND 
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from front oxygen 
(A/F) sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between ECM and 
chassis ground.

Connector & terminal

(B135) No. 9 (+) — Chassis ground (–):
(B135) No. 8 (+) — Chassis ground (–):

Is the voltage 8 V or more?

Repair the short 
circuit to power in 
the harness 
between ECM and 
front oxygen (A/F) 
sensor connector.

Replace the front 
oxygen (A/F) sen-
sor. <Ref. to 
FU(H4DOTC)-46, 
Front Oxygen (A/F) 
Sensor.>