Subaru Legacy (2005 year). Manual - part 132

EN(H4SO 2.0)(diag)-117

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

5

CHECK EXHAUST SYSTEM.
Check exhaust system parts.

NOTE:

Check the following items.
• Loose part and incomplete installation of 
exhaust system
• Damage (crack, hole etc.) of parts
• Looseness and ill fitting of parts between 
front oxygen (A/F) sensor and rear oxygen 
sensor

Is there any fault in exhaust 
system?

Repair or replace 
faulty parts.

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)-118

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

U: DTC P0138 O2 SENSOR CIRCUIT HIGH VOLTAGE (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:

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)-119

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK ANY OTHER DTC ON DISPLAY.

Is any other DTC displayed?

Check DTC using 
“List of Diagnostic 
Trouble Code 
(DTC)”. <Ref. to 
EN(H4SO 
2.0)(diag)-64, List 
of Diagnostic Trou-
ble Code (DTC).>

NOTE:
In this case, it is
not necessary to
inspect DTC
P0138.

Go to step 2.

2

CHECK REAR OXYGEN SENSOR DATA.
1) Warm-up the engine until engine coolant 
temperature is above 70

°C (158°F), and lower 

the engine speed rapidly from 5,000 rpm.
2) Read the data of rear oxygen sensor signal 
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 voltage more than 250 
mV?

Go to step 5.

Go to step 3.

3

CHECK HARNESS BETWEEN ECM AND 
REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM and 
rear oxygen sensor.
3) Measure the resistance of harness 
between ECM and rear oxygen sensor con-
nector.

Connector & terminal

(B136) No. 19 — (B19) No. 4:
(B136) No. 18 — (B19) No. 3:

Is the resistance more than 3 
Ω?

Repair the open 
circuit of harness 
between ECM and 
rear oxygen sen-
sor connector.

Go to step 4.

4

CHECK HARNESS BETWEEN REAR OXY-
GEN SENSOR AND ECM CONNECTOR.
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 harness connector and chassis ground.

Connector & terminal

(B19) No. 4 (+) — Chassis ground (

−

):

Is the voltage 0.2 — 0.5 V?

Replace the rear 
oxygen sensor. 
<Ref. to FU(H4SO 
2.0)-33, Rear Oxy-
gen Sensor.>

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

EN(H4SO 2.0)(diag)-120

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

5

CHECK EXHAUST SYSTEM.
Check exhaust system parts.

NOTE:

Check the following items.
• Loose part and incomplete installation of 
exhaust system
• Damage (crack, hole etc.) of parts
• Looseness and ill fitting of parts between 
front oxygen (A/F) sensor and rear oxygen 
sensor

Is there any fault in exhaust 
system?

Repair or replace 
faulty parts.

Replace the rear 
oxygen sensor. 
<Ref. to FU(H4SO 
2.0)-33, Rear Oxy-
gen Sensor.>

Step

Check

Yes

No