Subaru Legacy IV (2008 year). Manual - part 586

EN(H6DO)(diag)-317

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

DZ:DTC P2098 POST CATALYST FUEL TRIM SYSTEM TOO LEAN BANK 2

NOTE:
Refer to DTC P2099 for diagnostic procedure. <Ref. to EN(H6DO)(diag)-318, DTC P2099 POST CATALYST
FUEL TRIM SYSTEM TOO RICH BANK 2, Diagnostic Procedure with Diagnostic Trouble Code (DTC).>

17

CHECK FRONT OXYGEN (A/F) SENSOR 
AND REAR OXYGEN SENSOR DATA.
1) Warm up the engine until engine coolant 
temperature is higher than 75°C (167°F), then 
keep the engine idling for 5 minutes or more.
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(H6DO)(diag)-34, Subaru Select Moni-
tor.>
• General Scan Tool
For detailed operation procedures, refer to the
general scan tool operation manual.

Is a voltage of 0.8 V or more 
maintained for 5 minutes or 
more?

Replace the front 
oxygen (A/F) sen-
sor. <Ref. to 
FU(H6DO)-32,
Front Oxygen (A/F) 
Sensor.>

Go to step 18.

18

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

Connector & terminal

(B135) No. 4 — (E61) No. 3:
(B135) No. 30 — (E61) No. 4:

Is the resistance less than 1 

:? Go to step 19.

Repair the harness 
and connector.

NOTE:
In this case, repair
the following item:
• Open circuit in
harness between
ECM and rear oxy-
gen sensor con-
nector
• Poor contact of
coupling connector

19

CHECK HARNESS BETWEEN ECM AND 
REAR OXYGEN SENSOR CONNECTOR.
1) Connect the connector to ECM.
2) Turn the ignition switch to ON.
3) Measure the voltage between rear oxygen 
sensor connector and chassis ground.

Connector & terminal

(E61) No. 3 (+) — Chassis ground (–):

Is the voltage 0.2 — 0.5 V?

Replace the rear 
oxygen sensor. 
<Ref. to 
FU(H6DO)-34,
Rear Oxygen Sen-
sor.>

Repair the harness 
and connector.

NOTE:
In this case, repair
the following item:
• Open circuit of
harness between
the ECM and rear
oxygen sensor
• Poor contact in
ECM connector
• Poor contact of
coupling connector

Step

Check

Yes

No

EN(H6DO)(diag)-318

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

EA:DTC P2099 POST CATALYST FUEL TRIM SYSTEM TOO RICH BANK 2

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H6DO)-190, DTC P2099 POST CATALYST FUEL TRIM SYS-
TEM TOO RICH BANK 2, Diagnostic Trouble Code (DTC) Detecting Criteria.>

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H6DO)(diag)-52,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H6DO)(diag)-44, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:

SBF-5

BATTERY

E

E3

B22

B47

1

2

3

5

4

6

MAIN RELAY

E3

B22

8

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

*

3

4

5

6

1

2

B47

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

B22

3 4

1 2

E47

E24

16

10 11 12 13 14 15

25

24

30

9

8

7

17 18 19 20
28

21 22 23

29

32

31

1

2

3

4

5

6

27

26

33 34 35

B136

C:

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

B137

D:

1 2 3 4
5 6 7 8

B138

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

B135

B:

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

B134

A:

B11

2

E24

FRONT 

OXYGEN (A/F) 

SENSOR LH

3

4

B10

1

B7

B6

C2

C3

B8

4

1

3

B9

ECM

B135

B:

B134

A:

B137

D:

B136

C:

D3

A3

D2

D1

D7

A5

35

34

52

36

37

B21

E2

E

E

EN-06867

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

2

E47

FRONT 

OXYGEN (A/F) 

SENSOR RH

5

6

7

4

2

1

3

B138

*

*

B1

EN(H6DO)(diag)-319

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

B47

3

4

5

6

1

2

B22

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

1 2 3 4
5 6 7 8

B83

B138

3 4

1 2

E25

E61

B47

1

2

3

5

4

6

E3

B22

14

MAIN RELAY

2

4

3

1

E25

13

15

16

E3

B22

10

11

12

9

SBF-5

BATTERY

2

E61

4

3

1

*

1

*

1

*

1

B83

B138

ECM

B134

A:

B135

B:

B136

C:

B137

D3

A3

D2

D1

D7

A5

D:

C5

*

*

2

2

C4

E

B1

B15

B4

B30

35

34

52

36

37

B21

E2

E

E

 : TERMINAL No. OPTIONAL ARRANGEMENT

*

1

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

*

2

EN-06868

16

10 11 12 13 14 15

25

24

30

9

8

7

17 18 19 20
28

21 22 23

29

32

31

1

2

3

4

5

6

27

26

33 34 35

B136

C:

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

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

29 30 31

32 33

34 35

B135

B:

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

B134

A:

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

REAR
OXYGEN 
SENSOR LH

REAR
OXYGEN 
SENSOR RH

EN(H6DO)(diag)-320

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(H6DO)(diag)-
81, 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. 11 — (E24) No. 3:
(B135) No. 10 — (E24) No. 4:

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. 11 — Chassis ground:
(B135) No. 10 — 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

(E24) No. 3 (+) — 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

(E24) No. 4 (+) — 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

(E24) No. 3 (+) — Chassis ground (–):
(E24) No. 4 (+) — 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(H6DO)-38,
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.