Subaru Legacy III (2000-2003 year). Manual - part 122

EN(H4SO)-100

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

6

CHECK POWER SUPPLY TO REAR OXY-
GEN SENSOR.
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 connector and engine ground or chas-
sis ground.

Connector & terminal

(T6) No. 2 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

10 V

Go to step 7.

Repair power sup-
ply line.

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

7

CHECK REAR OXYGEN SENSOR.
1) Turn ignition switch to OFF.
2) Measure resistance between rear oxygen 

sensor connector terminals.

Terminals

No. 1 — No. 2:

Is the measured value less than the speci-
fied value?

30 

Ω

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
• Poor contact in 
coupling connector

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

Step

Value

Yes

No

EN(H4SO)-101

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

MEMO:

EN(H4SO)-102

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

E: DTC P0038 — HO2S HEATER CONTROL CIRCUIT HIGH (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)-103

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK INPUT SIGNAL FOR ECM.
Measure voltage between ECM connector and 
chassis ground.

Connector & terminal

(B136) No. 4 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the specified 
value?

8 V

Go to step 2.

Go to step 3.

2

CHECK CURRENT DATA.
1) Turn ignition switch to OFF.
2) Repair battery short circuit in harness 

between ECM and rear oxygen sensor con-
nector.

3) Turn ignition switch to ON.
4) Read data of rear oxygen sensor heater 

current using Subaru Select Monitor or the 
OBD-II general scan tool.
Does the measured value exceed the spec-
ified value?

NOTE:

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

7 A

Replace ECM.  
<Ref. to 
FU(H4SO)-45, 
Engine Control 
Module.>

END

3

CHECK POOR CONTACT.
Check poor contact in ECM connector. 
Is there poor contact in ECM connector?

There is poor contact.

Repair poor con-
tact in ECM con-
nector.

END