Subaru Legacy III (2000-2003 year). Manual - part 476

EN(H4DOSTC)-74

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

6

CHECK POWER SUPPLY TO REAR OXY-
GEN SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from rear oxygen 

sensor.

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

sensor connector and engine ground or 
chassis ground.

Connector & terminal

(T6) No. 2 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

10 V

Go to step 7.

Repair the power 
supply 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 the ignition switch to OFF.
2) Measure the resistance between rear oxy-

gen sensor connector terminals.

Terminals

No. 1 — No. 2:

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

30 

Ω

Repair the har-
ness and connec-
tor.

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 the rear 
oxygen sensor.  
<Ref. to 
FU(H4DOSTC)-
39, Rear Oxygen 
Sensor.>

Step

Value

Yes

No

EN(H4DOSTC)-75

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

MEMO:

EN(H4DOSTC)-76

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

D: DTC P0038 — HO2S HEATER CONTROL CIRCUIT HIGH (BANK 1 SENSOR 

2) —

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(H4DOSTC)-35, 
OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H4DOSTC)-33, Inspection 
Mode.> .
• WIRING DIAGRAM:

EN-00934

BATTERY

MAIN  RELAY

B47

1

2

3

5

4

6

E

E

E3

3

3
6

B22

B122

3

4

1

2

5

6

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

B22

B135

B136

B122

B47

T5

B137

1

2

7

8

9

5

6

3

4

10 11 12

19 20 21
29 30 31

13 14 15 16 17

27 28

18

22 23 24 25 26

1

4

2

3

T6

         REAR
OXYGEN SENSOR

D8

D9

C13

B17

B26

B19

ECM

B136

B137

C :

B135

B :

D :

1 2 3 4 5 6

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

1 2

7

8 9

5

6

3

4

10 11 12
19 20 21

13 14 15 16

17 18

22 23 24

1

2

3

4

2

4

3

1

T5

B19

T5

B19

T6

2 1
4 3

EN(H4DOSTC)-77

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

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

Connector & terminal

(B136) No. 13 (+) — 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 the ignition switch to OFF.
2) Repair the battery short circuit in harness 

between ECM and rear oxygen sensor con-
nector.

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

current using Subaru Select Monitor.
Does the measured value exceed the spec-
ified value?

NOTE:

For detailed operation procedure, refer to the
“READ CURRENT DATA FOR ENGINE”. <Ref.
to EN(H4DOSTC)-26, Subaru Select Monitor.>  

7 A

Replace the ECM.  
<Ref. to 
FU(H4DOSTC)-
40, Engine Con-
trol Module.>

END

3

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

There is poor contact.

Repair the poor 
contact in ECM 
connector.

END