Subaru Legacy III (2000-2003 year). Manual - part 136

EN(H4SO)-156

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Y: DTC P0138 — O2 SENSOR CIRCUIT HIGH VOLTAGE (BANK 1 SENSOR 2) —

• DTC DETECTING CONDITION:

• Two consecutive driving cycles with fault

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode<Ref. to EN(H4SO)-47, OPER-
ATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4SO)-40, OPERATION, Inspection 
Mode.> .
• WIRING DIAGRAM:

EN-01122

BATTERY

F44

B61

6

T5

B19

2

B47

MAIN RELAY

1

2

3

5

4

6

F44

1 2 3 4
5 6 7 8

C4

B14

B19

D15

C16

C5

REAR 

OXYGEN SENSOR

ECM

4

1

3

1

4

3

2

8

B22

B83

B19

T5

T6

E3

B47

B19

B22

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

3

4

5

6

1

2

T6

4 3

2 1

2

1

FG

3

B135

B:

C: B136

D: B137

SBF-5

B136

5 6

7

2

1

9

8

4

3

23

21 22

24

10 11 12 13 14

25 26

15 16 17

18 19 20

B137

4

1
5

3

2
6

18

15

16

7 8 9 10 11

17

19 20

12 13

14

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

B135

B83

1 2 3 4 5 6

4

EG

: FOR G.C.C COUNTRIES MODEL 

: EXCEPT FOR G.C.C COUNTRIES MODEL 

FG

EG

EN(H4SO)-157

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK ANY OTHER DTC ON DISPLAY.
Does the Subaru Select Monitor or OBD-II 
general scan tool indicate DTC P0130, P0131, 
P0132 or P0134?

DTC indicated.

Check DTC refer-
ring "List of Diag-
nostic Trouble 
Code (DTC)".  
<Ref. to 
EN(H4SO)-83, List 
of Diagnostic 
Trouble Code 
(DTC).>

NOTE:
In this case,
CHECKING proce-
dure for P0138 is
not necessary.

Go to step 3.

2

CHECK REAR OXYGEN SENSOR DATA.
1) Warm-up the engine until engine coolant 

temperature is above 70

°

C (158

°

F), and 

race engine until the engine speed reaches 
to 5,000 rpm and release accelerator pedal 
rapidly.

2) Read data of rear oxygen sensor signal 

using Subaru Select Monitor or OBD-II gen-
eral scan tool.
Does the value fluctuate?

NOTE:

•Subaru Select Monitor
For detailed operation procedure, refer to the 
“READ CURRENT DATA SHOWN ON DIS-
PLAY FOR ENGINE”. <Ref. to EN(H4SO)-32, 
Subaru Select Monitor.>
•OBD-II general scan tool
For detailed operation procedures, refer to the 
OBD-II General Scan Tool Instruction Manual.

250 mV

Go to step 5.

Go to step 3.

3

CHECK HARNESS BETWEEN ECM AND 
REAR OXYGEN SENSOR CONNECTOR.
1) Turn ignition switch to OFF.
2) Disconnect connectors from ECM and rear 

oxygen sensor.

3) Measure resistance of harness between 

ECM and rear oxygen sensor connector.

Connector & terminal

(B135) No. 14 — (T6) No. 4:
(B135) No. 19 — (T6) No. 3:

Does the measured value exceed the spec-
ified value?

3 

Ω

Repair open circuit 
in harness 
between ECM and 
rear oxygen sen-
sor connector.

Go to step 4.

4

CHECK HARNESS BETWEEN REAR OXY-
GEN SENSOR AND ECM CONNECTOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from rear oxygen 

sensor.

3) Turn ignition switch to ON.
4) Measure voltage between rear oxygen sen-

sor harness connector and engine ground 
or chassis ground.

Connector & terminal

(T6) No. 4 (+) — Engine ground (

−−−−

):

Is the measured value within the specified 
range?

0.2 V - 0.5 V

Replace rear oxy-
gen sensor. <Ref. 
to FU(H4SO)-43, 
Rear Oxygen Sen-
sor.>

Repair harness 
and connector.

NOTE:
In this case, repair
the following:
• Open circuit in 
harness between 
rear oxygen sen-
sor and ECM con-
nector
• Poor contact in 
rear oxygen sen-
sor connector
• Poor contact in 
ECM connector

EN(H4SO)-158

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

5

CHECK EXHAUST SYSTEM.
Check exhaust system parts.
Is there a fault in exhaust system?

NOTE:

Check the following items.
•Loose installation of portions
•Damage (crack, hole etc.) of parts
•Looseness and ill fitting of parts between front 
oxygen (A/F) sensor and rear oxygen sensor

There is a fault.

Repair or replace 
faulty parts.

Replace rear oxy-
gen sensor. <Ref. 
to FU(H4SO)-43, 
Rear Oxygen Sen-
sor.>

Step

Value

Yes

No

EN(H4SO)-159

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

MEMO: