Subaru Legacy IV (2008 year). Manual - part 320

EN(H4DOTC)(diag)-101

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

I:

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(H4DOTC)-22, 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(H4DOTC)(diag)-
52, OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4DOTC)(diag)-43, PRO-
CEDURE, Inspection Mode.>.
WIRING DIAGRAM:

EN-05670

B83

1 2 3 4
5 6 7 8

B138

B47

1

2

4

6

3

5

E

*

*

B138

B83

3

4

1

2

5

6

B135

B47

B19

B136

B:

C:

B137

D:

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

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

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

B19

T5

2

2

T5

B19

3

1

4

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

T6

SBF-5

*

1

*

2

1
1

*

*

2
2

C4

B4

B30

B1

B134

T6

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:

B135

B:

B136

C:

B137

D:

A:

D2

A5

D3

E2

B21

E

35

34

40

D7

36

D1

37

1 2
3 4

3

1

4

MAIN RELAY

REAR
OXYGEN SENSOR

BATTERY

ECM

: TERMINAL No. OPTIONAL 
  ARRANGEMENT

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

EN(H4DOTC)(diag)-102

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(H4DOTC)(diag)-103

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

J: DTC P0068 MAP/MAF - THROTTLE POSITION CORRELATION

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H4DOTC)-24, 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(H4DOTC)(diag)-
52, OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4DOTC)(diag)-43, PRO-
CEDURE, Inspection Mode.>.
WIRING DIAGRAM:

EN-05671

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

23

28

6

B21

E2

2

3

1

E21

E21

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

1 2 3

6

29

19

MANIFOLD

ABSOLUTE
PRESSURE

SENSOR

ECM

EN(H4DOTC)(diag)-104

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(H4DOTC)(diag)-34, 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(H4DOTC)-
37, Manifold Abso-
lute Pressure Sen-
sor.>

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(H4DOTC)(diag)-34, 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(H4DOTC)-14, 
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(H4DOTC)-
37, Manifold Abso-
lute Pressure Sen-
sor.>

Replace the elec-
tronic throttle con-
trol. <Ref. to 
FU(H4DOTC)-14, 
Throttle Body.>