Subaru Legacy IV (2008 year). Service manual - part 123

EN(H4SO)(diag)-95

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

E: DTC P0032 HO2S HEATER CONTROL CIRCUIT HIGH (BANK 1 SENSOR 1)

DTC DETECTING CONDITION:
• Immediately at fault recognition
• GENERAL DESCRIPTION <Ref. to GD(H4SO)-15, DTC P0032 HO2S HEATER CONTROL CIRCUIT
HIGH (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(H4SO)(diag)-50,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4SO)(diag)-41, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:

EN-06835

B137

8

5

6

10 11 12 13 14 15

7

2

1

3

4

16

30

19 20

22
28 29

9

17

18

25

21

23

24

31

26 27

3

4

1

2

5

6

B327

SBF-5

E

E

E

B327

E22

6

4

5

3

2
1

6

4

1

3

B1

B9

B8

C3

C2

A5

D7

D1

D2

D3

36

52

34

35

37

B134

A:

B135

B:

B136

C:

B137

D:

B21

E2

ECM

B21

E2

50

51

3

4

E2

B21

E

E22

B138

B134

B135

A:

B:

B136

C:

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

BATTERY

FRONT OXYGEN 

(A/F) SENSOR

A/F, OXYGEN 
SENSOR RELAY

B138

*

*

 : TERMINAL No. OPTIONAL  
 ARRANGEMENT

*

3

1

6 5 4

2

5

6

7

2

1

3

4

29

10 11 12 13 14 15

25

24

16

30

9

8

17 18 19

20
28

21 22 23

32

31

26 27

33

34 35

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

3 4

5 6

1 2

7 8

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

EN(H4SO)(diag)-96

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK HARNESS BETWEEN ECM AND 
FRONT OXYGEN (A/F) SENSOR.
1) Turn the ignition switch to OFF.
2) Measure the voltage between ECM and 
chassis ground.

Connector & terminal

(B136) No. 2 (+) — Chassis ground (–):
(B136) No. 3 (+) — Chassis ground (–):

Is the voltage 10 V or more?

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

Go to step 2.

2

CHECK GROUND CIRCUIT FOR ECM.
1) Disconnect the connectors from ECM.
2) Measure the resistance between ECM and 
chassis ground.

Connector & terminal

(B134) No. 5 — Chassis ground:
(B137) No. 1 — Chassis ground:
(B137) No. 2 — Chassis ground:
(B137) No. 3 — Chassis ground:
(B137) No. 7 — Chassis ground:

Is the resistance less than 5 

:? Repair the poor 

contact of ECM 
connector.

Repair the harness 
and connector.

NOTE:
In this case, repair
the following item:
• Open circuit of
harness between
ECM and engine
ground
• Poor contact of
coupling connector

EN(H4SO)(diag)-97

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

F: DTC P0037 HO2S HEATER CONTROL CIRCUIT LOW (BANK 1 SENSOR 2)

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H4SO)-17, DTC P0037 HO2S HEATER CONTROL CIRCUIT
LOW (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(H4SO)(diag)-50,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4SO)(diag)-41, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:

EN-06836

A5

D1

D2

D3

D7

36

34

35

37

52

ECM

B21

B138

E2

B135

B:

D: B137

C: B136

E

E

A: B134

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

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

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

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

A:

B:

C:

D:

*

*

3

4

1

2

5

6

B327

SBF-5

E

B327

E23

6

4

5

3

2
1

1

B21

E2

50

53

1

19

E2

B21

E

E23

BATTERY

REAR OXYGEN 

SENSOR

A/F, OXYGEN 
SENSOR RELAY

1
3 4

2

2

3

4

B1

B4

A29

C4

B138

3 4

5 6

1 2

7 8

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

 : TERMINAL No. OPTIONAL  
 ARRANGEMENT

*

EN(H4SO)(diag)-98

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK POWER SUPPLY TO REAR OXY-
GEN 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 engine ground.

Connector & terminal

(E23) No. 2 (+) — Engine ground (–):

Is the voltage 10 V or more?

Go to step 2.

Repair the power 
supply line. Or 
replace the main 
relay.

NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
A/F, oxygen sen-
sor relay connector
and rear oxygen
sensor connector
• Poor contact of
A/F, oxygen sen-
sor relay connector
• Poor contact of
coupling connector

2

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

Connector & terminal

(B136) No. 4 — (E23) No. 1:

Is the resistance less than 1 

:? Go to step 3.

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

3

CHECK GROUND CIRCUIT FOR ECM.
Measure the resistance of harness between 
ECM and chassis ground.

Connector & terminal

(B134) No. 5 — Chassis ground:
(B137) No. 1 — Chassis ground:
(B137) No. 2 — Chassis ground:
(B137) No. 3 — Chassis ground:
(B137) No. 7 — Chassis ground:

Is the resistance less than 5 

:? Go to step 4.

Repair the harness 
and connector.

NOTE:
In this case, repair
the following item:
• Open circuit of
harness between
ECM and engine
ground
• Poor contact in
ECM connector
• Poor contact of
coupling connector

4

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

Terminals

No. 2 — No. 1:

Is the resistance between 5 — 
7

:?

Repair the poor 
contact of ECM 
connector.

Replace the rear 
oxygen sensor. 
<Ref. to 
FU(H4SO)-37,
Rear Oxygen Sen-
sor.>