Subaru Legacy (2005 year). Manual - part 122

EN(H4SO 2.0)(diag)-77

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

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

(B135) No. 5 — Chassis ground:
(B135) No. 6 — Chassis ground:

Is the resistance less than 5 
Ω?

Go to step 2.

Repair the har-
ness and connec-
tor.

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

2

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(H4SO 2.0)(diag)-25, Subaru Select 
Monitor.>
• 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 item:
• Poor contact in 
rear oxygen sen-
sor connector
• Poor contact in 
rear oxygen sen-
sor connecting 
harness connector
• Poor contact in 
ECM connector

Go to step 3.

3

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

Connector & terminal

(B134) No. 1 (+) — Chassis ground (

−

):

Is the voltage less than 1 V?

Go to step 6.

Go to step 4.

4

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

Connector & terminal

(B134) No. 1 (+) — 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 5.

5

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

(B134) No. 1 (+) — Chassis ground (

−

):

Is the voltage less than 1 V?

Replace the ECM. 
<Ref. to FU(H4SO 
2.0)-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(H4SO 2.0)-34, 
Engine Control 
Module (ECM).>

EN(H4SO 2.0)(diag)-78

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

6

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

(B19) No. 2 (+) — Chassis ground (

−

):

Is the voltage more than 10 V? Go to step 7.

Repair the power 
supply line.

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

7

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

Terminals

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 item:
• 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(H4SO 
2.0)-33, Rear Oxy-
gen Sensor.>

Step

Check

Yes

No

EN(H4SO 2.0)(diag)-79

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

E: 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, perform Clear Memory Mode <Ref. to EN(H4SO 2.0)(diag)-
38, OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO 2.0)(diag)-32, PRO-
CEDURE, Inspection Mode.>.
WIRING DIAGRAM:

Step

Check

Yes

No

1

CHECK INPUT SIGNAL OF ECM.
Measure the voltage between ECM connector 
and chassis ground.

Connector & terminal

(B134) No. 1 (+) — Chassis ground (

−

):

Is the voltage more than 8 V?

Go to step 2.

Go to step 3.

EN-03476

B47

T5

3

4

5

6

1

2

1 2
3 4

BATTERY

B47

MAIN RELAY

1

2

4

6

3

5

A1

C19

C18

C30

B5

B6

REAR 
OXYGEN SENSOR

ECM

1

4

3

2

52

B21

T5

E2

1

B135

B:

SBF-5

C: B136

E

E

A: B134

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:

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

1 2 3 4
5 6 7 8

B138

B83

1

T5

B19

2

2

B19

B83

B138

:LHD

:RHD

*

*

*

*

1

*

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

2

*

: TERMINAL No. RANDOM
  ARRANGEMENT AMONG
  3,4,7, AND 8

EN(H4SO 2.0)(diag)-80

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

2

CHECK CURRENT DATA.
1) Turn the ignition switch to OFF.
2) Repair the battery short circuit of harness 
between ECM and rear oxygen sensor con-
nector.
3) Turn the ignition switch to ON.
4) 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(H4SO 2.0)(diag)-25, Subaru Select 
Monitor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the current more than 7 A?

Replace the ECM. 
<Ref. to FU(H4SO 
2.0)-34, Engine 
Control Module 
(ECM).>

Finish the diagno-
sis.

3

CHECK POOR CONTACT.
Check poor contact in ECM connector.

Is there poor contact in ECM 
connector?

Repair the poor 
contact in ECM 
connector.

Finish the diagno-
sis.

Step

Check

Yes

No