Subaru Legacy (2005 year). Service 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