Subaru Legacy IV (2008 year). Service manual - part 124

EN(H4SO)(diag)-99

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

G: DTC P0038 HO2S HEATER CONTROL CIRCUIT HIGH (BANK 1 SENSOR 2)

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H4SO)-19, DTC P0038 HO2S HEATER CONTROL CIRCUIT
HIGH (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)-100

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK HARNESS BETWEEN ECM AND 
REAR OXYGEN SENSOR.
1) Turn the ignition switch to OFF.
2) Measure the voltage between ECM and 
chassis ground.

Connector & terminal

(B136) No. 4 (+) — Chassis ground (–):

Is the voltage 10 V or more?

Repair the short 
circuit to power in 
the harness 
between ECM and 
rear oxygen 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)-101

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

H: DTC P0068 MAP/MAF - THROTTLE POSITION CORRELATION

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H4SO)-21, DTC P0068 MAP/MAF - THROTTLE POSITION
CORRELATION, 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-04029

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

19

20

7

B21

E2

2

3

1

E21

E21

ECM

B21

B134

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

B134

MANIFOLD

ABSOLUTE
PRESSURE

SENSOR

1 2 3

29

6

19

EN(H4SO)(diag)-102

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK AIR INTAKE SYSTEM.

Are there holes, loose bolts or 
disconnection of hose on air 
intake system?

Repair the air 
intake system.

Go to step 2.

2

CHECK MANIFOLD ABSOLUTE PRESSURE 
SENSOR.
1) Start the engine and warm up engine until 
coolant temperature is higher than 75°C 
(167°F).
2) For AT models, set the select lever to “P” 
range or “N” range, and for MT models, place 
the shift lever in the neutral position.
3) Turn the A/C switch to OFF.
4) Turn all the accessory switches to OFF.
5) Read the data of intake manifold pressure 
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)(diag)-33, Subaru Select Moni-
tor.>
• General Scan Tool
For detailed operation procedures, refer to the
“General Scan Tool Instruction Manual”.

Is the measured value 73.3 — 
106.6 kPa (550 — 800 mmHg, 
21.65 — 31.50 inHg) when the 
ignition is turned ON, and 20.0 
— 46.7 kPa (150 — 350 mmHg, 
5.91 — 13.78 inHg) during 
idling?

Go to step 3.

Replace the mani-
fold absolute pres-
sure sensor. <Ref. 
to FU(H4SO)-27, 
Manifold Absolute 
Pressure Sensor.>

3

CHECK THROTTLE OPENING ANGLE.
Read the data of throttle position 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)(diag)-33, Subaru Select Moni-
tor.>
• General Scan Tool
For detailed operation procedures, refer to the
“General Scan Tool Instruction Manual”.

Is the measured value less than 
5% when throttle is fully 
closed?

Go to step 4.

Replace the elec-
tronic throttle con-
trol. <Ref. to 
FU(H4SO)-12,
Throttle Body.>

4

CHECK THROTTLE OPENING ANGLE.

Is the measured value 85% or 
more when throttle is fully 
open?

Replace the mani-
fold absolute pres-
sure sensor. <Ref. 
to FU(H4SO)-27, 
Manifold Absolute 
Pressure Sensor.>

Replace the elec-
tronic throttle con-
trol. <Ref. to 
FU(H4SO)-12,
Throttle Body.>