Subaru Legacy IV (2008 year). Manual - part 167

EN(H4SO)(diag)-271

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

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)-272

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK FOR ANY OTHER DTC ON DISPLAY. Is any other DTC displayed?

Check DTC using 
“List of Diagnostic 
Trouble Code 
(DTC)”. <Ref. to 
EN(H4SO)(diag)-
80, List of Diagnos-
tic Trouble Code 
(DTC).>

Go to step 2.

2

CHECK FRONT OXYGEN (A/F) SENSOR 
CONNECTOR AND COUPLING CONNEC-
TOR.

Has water entered the connec-
tor?

Completely 
remove any water 
inside.

Go to step 3.

3

CHECK HARNESS BETWEEN ECM AND 
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM and 
front oxygen (A/F) sensor.
3) Measure the resistance of harness between 
ECM and front oxygen (A/F) sensor connector.

Connector & terminal

(B135) No. 9 — (E22) No. 1:
(B135) No. 8 — (E22) No. 3:

Is the resistance less than 1 

:? Go to step 4.

Repair the harness 
and connector.

NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM and front oxy-
gen (A/F) sensor
connector
• Poor contact of
coupling connector

4

CHECK HARNESS BETWEEN ECM AND 
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
Measure the resistance between ECM and 
chassis ground.

Connector & terminal

(B135) No. 9 — Chassis ground:
(B135) No. 8 — Chassis ground:

Is the resistance 1 M

: or 

more?

Go to step 5.

Repair the ground 
short circuit of har-
ness between 
ECM and front oxy-
gen (A/F) sensor 
connector.

5

CHECK OUTPUT SIGNAL FOR ECM.
1) Connect the connector to ECM.
2) Turn the ignition switch to ON.
3) Measure the voltage between front oxygen 
(A/F) sensor connector and chassis ground.

Connector & terminal

(E22) No. 1 (+) — Chassis ground (–):

Is the voltage 4.5 V or more?

Go to step 7.

Go to step 6.

6

CHECK OUTPUT SIGNAL FOR ECM.
Measure the voltage between front oxygen (A/F) 
sensor connector and chassis ground.

Connector & terminal

(E22) No. 3 (+) — Chassis ground (–):

Is the voltage 4.95 V or more?

Go to step 7.

Go to step 8.

7

CHECK OUTPUT SIGNAL FOR ECM.
Measure the voltage between front oxygen (A/F) 
sensor connector and chassis ground.

Connector & terminal

(E22) No. 1 (+) — Chassis ground (–):
(E22) No. 3 (+) — Chassis ground (–):

Is the voltage 8 V or more?

Repair the short 
circuit to power in 
the harness 
between ECM and 
front oxygen (A/F) 
sensor connector. 
After repair, 
replace the ECM. 
<Ref. to 
FU(H4SO)-39, 
Engine Control 
Module (ECM).>

Repair the poor 
contact of ECM 
connector.

8

CHECK EXHAUST SYSTEM.

Are there holes or loose bolts 
on exhaust system?

Repair the exhaust 
system.

Go to step 9.

EN(H4SO)(diag)-273

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

9

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 10.

10

CHECK FUEL PRESSURE.

WARNING:
Place “NO OPEN FLAMES” signs near the
working area.

CAUTION:
Be careful not to spill fuel.
1) Connect the front oxygen (A/F) sensor con-
nector.
2) Measure the fuel pressure. <Ref. to 
ME(H4SO)-26, INSPECTION, Fuel Pressure.>

CAUTION:
Release fuel pressure before removing the
fuel pressure gauge.

Is the measured value 339.5 — 
360.5 kPa (3.5 — 3.7 kg/cm

2

,

49 — 52 psi)?

Go to step 11.

Repair the follow-
ing item.
Fuel pressure is 
too high:
• Clogged fuel line 
or bent hose
Fuel pressure is 
too low:
• Improper fuel 
pump discharge
• Clogged fuel line

11

CHECK ENGINE COOLANT TEMPERATURE 
SENSOR.
1) Start the engine and warm up completely.
2) Read the data of engine coolant tempera-
ture 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 operation manual.

Is the engine coolant tempera-
ture 75°C (167°F) or higher?

Go to step 12.

Replace the 
engine coolant 
temperature sen-
sor. <Ref. to 
FU(H4SO)-22,
Engine Coolant 
Temperature Sen-
sor.>

12

CHECK MASS AIR FLOW AND INTAKE AIR 
TEMPERATURE 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 the mass air flow and 
intake air temperature sensor signal using Sub-
aru 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 operation manual.

Is the measured value 2.0 — 
5.0 g/s (0.26 — 0.66 lb/m)?

Go to step 13.

Replace the mass 
air flow and intake 
air temperature 
sensor. <Ref. to 
FU(H4SO)-28,
Mass Air Flow and 
Intake Air Temper-
ature Sensor.>

Step

Check

Yes

No

EN(H4SO)(diag)-274

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

13

CHECK MASS AIR FLOW AND INTAKE AIR 
TEMPERATURE 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) Open the front hood.
6) Measure the ambient temperature.
7) Read the data of the mass air flow and 
intake air temperature sensor signal using Sub-
aru 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 operation manual.

Subtract ambient temperature 
from intake air temperature. Is 
the obtained value –10 — 50°C 
(–18 — 90°F)?

Go to step 14.

Check the mass air 
flow and intake air 
temperature sen-
sor. <Ref. to 
FU(H4SO)-28,
Mass Air Flow and 
Intake Air Temper-
ature Sensor.>

14

CHECK REAR OXYGEN SENSOR DATA.
1) Warm up the engine until engine coolant 
temperature is above 75°C (167°F), and keep 
the engine speed at 3,000 rpm. (for up to 2 min-
utes)
2) Read the data of rear oxygen sensor signal 
using Subaru Select Monitor or general scan 
tool.

NOTE:
• Depress the clutch pedal. (MT model)
• 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 operation manual.

Is the voltage 490 mV or more? Go to step 15.

Go to step 16.

15

CHECK REAR OXYGEN SENSOR DATA.
1) Warm up the engine until engine coolant 
temperature is above 75°C (167°F), and rapidly 
reduce the engine speed from 3,000 rpm.
2) Read the data of rear oxygen sensor signal 
using Subaru Select Monitor or general scan 
tool.

NOTE:
• Depress the clutch pedal. (MT model)
• 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 operation manual.

Is the voltage 250 mV or less?

Go to step 17.

Go to step 16.

Step

Check

Yes

No