Subaru Legacy (2005 year). Manual — part 443

EN(H6DO)(diag)-85

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

H: DTC P0037 HO2S HEATER CONTROL CIRCUIT LOW (BANK 1 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

*

*

*

*

EN(H6DO)(diag)-86

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

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 chassis ground.

Connector & terminal

(E61) No. 2 (+) — Chassis ground (

−

):

Is the voltage more than 10 V? Go to step 2.

Repair the power
supply line.

NOTE:
In this case, repair
the following:
• Open circuit of
harness between
main relay and
rear oxygen sen-
sor connector
• Poor contact in
rear oxygen sen-
sor connector
• Poor contact in
main relay connec-
tor

2

CHECK GROUND CIRCUIT FOR ECM.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Measure the resistance of harness
between ECM connector and chassis ground.

Connector & terminal

(B134) No. 4 — Chassis ground:
(B134) No. 5 — Chassis ground:
(B134) No. 6 — Chassis ground:
(B134) No. 7 — Chassis ground:

Is the resistance less than 5
Ω?

Go to step 3.

Repair the har-
ness and connec-
tor.

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

3

CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of rear oxygen sensor heater
current 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)-26, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedure, refer to the
general scan tool operation manual.

Is the current more than 0.2 A? Repair the con-

nector.

NOTE:
In this case, repair
the following:
• Poor contact in
rear oxygen sen-
sor connector
• Poor contact in
coupling connector
• Poor contact in
ECM connector

Go to step 4.

4

CHECK OUTPUT SIGNAL FROM ECM.
1) Start and idle the engine.
2) Measure the voltage between ECM con-
nector and chassis ground.

Connector & terminal

(B135) No. 2 (+) — Chassis ground (

−

):

Is the voltage less than 1 V?

Go to step 7.

Go to step 5.

5

CHECK OUTPUT SIGNAL FROM ECM.
Measure the voltage between ECM connector
and chassis ground.

Connector & terminal

(B135) No. 2 (+) — Chassis ground (

−

):

Does the voltage change by
shaking the ECM harness and
connector while monitoring the
value of voltage meter?

Repair the poor
contact in ECM
connector.

Go to step 6.

EN(H6DO)(diag)-87

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

6

CHECK OUTPUT SIGNAL FROM ECM.
1) Disconnect the connector from rear oxygen
sensor.
2) Measure the voltage between ECM con-
nector and chassis ground.

Connector & terminal

(B135) No. 2 (+) — Chassis ground (

−

):

Is the voltage less than 1 V?

Replace the ECM.
<Ref. to
FU(H6DO)-34,
Engine Control
Module (ECM).>

Repair the battery
short circuit of har-
ness between
ECM and rear oxy-
gen sensor con-
nector. After
repair, replace the
ECM. <Ref. to
FU(H6DO)-34,
Engine Control
Module (ECM).>

7

CHECK REAR OXYGEN SENSOR.
1) Turn the ignition switch to OFF.
2) Measure the resistance between rear oxy-
gen sensor connector terminals.

Terminal

No. 1 — No. 2:

Is the resistance less than 30
Ω?

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
• Poor contact in
coupling connector

Replace the rear
oxygen sensor.
<Ref. to
FU(H6DO)-32,
Rear Oxygen Sen-
sor.>

Step

Check

Yes

No

EN(H6DO)(diag)-88

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

I:

DTC P0038 HO2S HEATER CONTROL CIRCUIT HIGH (BANK 1 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

*

*

*

*