Subaru Legacy (2005 year). Manual — part 129

EN(H4SO 2.0)(diag)-105

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).>

Go to step 2.

2

CHECK FRONT OXYGEN (A/F) SENSOR DA-
TA.
1) Start the engine.
2) While observing the Subaru Select Monitor
or general scan tool screen, warm-up the
engine until engine coolant temperature is
above 70

°C (160°F).

If the engine is already warmed-up, operate at
idle speed for at least 1 minute.
3) Read the data of front oxygen (A/F) 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 0.85 — 1.15 V?

Go to step 3.

Go to step 4.

3

CHECK FRONT OXYGEN (A/F) SENSOR DA-
TA.
1) Race the engine at speed from idling to
5,000 rpm for a total of 5 cycles.
2) Read the data of front oxygen (A/F) sensor
signal during racing using Subaru Select Moni-
tor or general scan tool.

NOTE:

• Air fuel ratio is rich at normal condition or
during racing.
• To increase engine speed to 5,000 rpm,
slowly depress accelerator pedal, taking
approximately 5 seconds, and quickly release
accelerator pedal to decrease engine speed.
• 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 1.1 V? Go to step 6.

Go to step 4.

EN(H4SO 2.0)(diag)-106

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

4

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

Connector & terminal
LHD model

(B136) No. 33 — (E24) No. 1:
(B136) No. 35 — (E24) No. 2:

RHD model

(B136) No. 33 — (E24) No. 4:
(B136) No. 35 — (E24) No. 6:

Is the resistance less than 5
Ω?

Go to step 5.

Repair the open
circuit between
ECM and front
oxygen (A/F) sen-
sor.

5

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

Connector & terminal

(B136) No. 33 — Chassis ground:
(B136) No. 35 — Chassis ground:

Is the resistance more than 1
M

Ω?

Go to step 6.

Repair the ground
short circuit
between ECM and
front oxygen (A/F)
sensor.

6

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 of front oxygen (A/F) sensor
• 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 front
oxygen (A/F) sen-
sor. <Ref. to
FU(H4SO 2.0)-32,
Front Oxygen (A/
F) Sensor.>

Step

Check

Yes

No

EN(H4SO 2.0)(diag)-107

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

P: DTC P0131 O2 SENSOR CIRCUIT LOW VOLTAGE (BANK 1 SENSOR 1)

DTC DETECTING CONDITION:
Immediately at fault recognition

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-03475

3

4

1

2

5

6

B47

SBF-5

E

B47

E24

5
3

4
6

2
1

C34

C35

C33

B3

B2

B1

B135

E

B5

B6

52

B21

E2

B21

E2

50

51

3

4

E2

B21

E

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

E24

ECM

BATTERY

FRONT OXYGEN

(A/F) SENSOR

MAIN RELAY

B136

B:

C:

1

2

3

4

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

B:

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

C:

E24

3

2

*

1

*

*

3

LHD : 4

RHD : 1

*

1

*

*

2

3

3

1

6 5 4

2

: RHD

: LHD

LHD : 1

RHD : 4

LHD : 2

RHD : 6

EN(H4SO 2.0)(diag)-108

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

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

Connector & terminal

(B136) No. 33 — Chassis ground:
(B136) No. 35 — Chassis ground:

Is the resistance more than 1
M

Ω?

Replace the front
oxygen (A/F) sen-
sor. <Ref. to
FU(H4SO 2.0)-32,
Front Oxygen (A/
F) Sensor.>

Repair the ground
short circuit of har-
ness between
ECM and front
oxygen (A/F) sen-
sor connector.