Subaru Legacy (2005 year). Manual - part 461

EN(H6DO)(diag)-157

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AN:DTC P0154 O2 SENSOR CIRCUIT NO ACTIVITY DETECTED (BANK 2 SEN-

SOR 1)

DTC DETECTING CONDITION:
Immediately at fault recognition

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.>.

Step

Check

Yes

No

1

CHECK ANY OTHER DTC ON DISPLAY.

Is any other DTC displayed?

Check DTC using 
the List of Diag-
nostic Trouble 
Code (DTC). <Ref. 
to 
EN(H6DO)(diag)-
66, List of Diag-
nostic Trouble 
Code (DTC).>

NOTE:
In this case, it is
not necessary to
inspect DTC
P0133.

Go to step 2.

2

CHECK EXHAUST SYSTEM.

NOTE:

Check the following items.
• Loose installation of front portion of exhaust 
pipe onto cylinder heads
• Loose connection between front exhaust 
pipe and front catalytic converter
• Damage of exhaust pipe resulting in a hole

Is there any fault in exhaust 
system?

Repair the exhaust 
system.

Replace the front 
oxygen (A/F) sen-
sor. <Ref. to 
FU(H6DO)-30, 
Front Oxygen (A/
F) Sensor.>

EN(H6DO)(diag)-158

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

WIRING DIAGRAM:

BATTERY

SBF-5

B47

MAIN RELAY

A4

A5

A6

A7

2

52

54

B21

E2

ECM

A34

A27

B7

A1

A2

A3

A26

A33

4

1

3

FRONT 

OXYGEN 

(A/F) 

SENSOR LH

E24

2

B135

B:

B134

A:

4

3

1

FRONT 

OXYGEN 

(A/F) 

SENSOR RH

E47

E3

B22

8

5

6

E3

B22

2

1

3

4

B47

3

4

5

6

1

2

A25

B22

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

3 4

1 2

E47

E24

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

B:

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:

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

E

E

EN-03494

B135

B:

B134

A:

7

5
3

EN(H6DO)(diag)-159

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

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

Connector & terminal

(B134) No. 27 — (E24) No. 4:
(B134) No. 34 — (E24) No. 3:

Is the resistance less than 1 
Ω?

Go to step 2.

Repair the har-
ness and connec-
tor.

NOTE:
In this case, repair
the following:
• Open circuit of 
harness between 
ECM and front 
oxygen (A/F) sen-
sor connector
• Poor contact in 
front oxygen (A/F) 
sensor connector
• Poor contact in 
ECM connector

2

CHECK POOR CONTACT.
Check poor contact in front oxygen (A/F) sen-
sor connector.

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

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

Replace the front 
oxygen (A/F) sen-
sor. <Ref. to 
FU(H6DO)-30, 
Front Oxygen (A/
F) Sensor.>

EN(H6DO)(diag)-160

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

AO:DTC P0157 O2 SENSOR CIRCUIT LOW VOLTAGE (BANK 2 SENSOR 2)

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

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:

BATTERY

SBF-5

B47

MAIN RELAY

A4

A5

A6

A7

2

52

54

B21

E2

ECM

B3

D31

D25

D24

B2

C35

4

3

1

REAR 

OXYGEN

SENSOR LH

E25

2

4

3

1

REAR 

OXYGEN 

SENSOR RH

E61

E3

B22

14

13

15

E3

B22

10

11

12

9

B83

B47

3

4

5

6

1

2

EN-03495

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

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

B:

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:

16

B134

A:

B135

B:

B136

C:

B137

D:

B22

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

B136

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

C:

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

D:

1 2 3 4
5 6 7 8

B83

3 4

1 2

E25

E61

E

E

5
3

: TERMINAL No. 
   RANDOM ARRANGEMENT

*

*

*

*