Subaru Legacy III (2000-2003 year). Manual - part 329

EN(H6DO)-118

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK GROUND CIRCUIT OF ECM.
Measure resistance of harness between ECM 
connector and chassis ground.

Connector & terminal

(B137) No. 31 — Chassis ground:
(B137) No. 21 — Chassis ground:
(B137) No. 8 — Chassis ground:
(B137) No. 9 — Chassis ground:

Is the measured value less than the specified 
value?

5 

Ω

Go to step 2.

Repair harness 
and connector.

NOTE:
In this case, repair
the following:
• Open circuit in 
harness between 
ECM and engine 
ground terminal
• Poor contact in 
ECM connector
Poor contact in 
coupling connector

2

CHECK CURRENT DATA.
1) Start engine
2) Read data of front oxygen (A/F) sensor 

heater current using Subaru Select Monitor 
or 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(H6DO)-34, Subaru Select Moni-
tor.>
• OBD-II scan tool
For detailed operation procedures, refer to the 
OBD-II General Scan Tool Instruction Manual.

0.2 A

Repair poor con-
tact in connector.

NOTE:
In this case, repair
the following:
• Poor contact in 
front oxygen (A/F) 
sensor connector
• Poor contact in 
ECM connector

Go to step 3.

3

CHECK OUTPUT SIGNAL FROM ECM.
1) Start and idle the engine.
2) Measure voltage between ECM connector 

and chassis ground.

Connector & terminal

(B137) No. 7 (+) — Chassis ground (

−−−−

):

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

1.0 V

Go to step 5.

Go to step 4.

4

CHECK OUTPUT SIGNAL FROM ECM.
Measure voltage between ECM connector and 
chassis ground.

Connector & terminal

(B137) No. 7 (+) — Chassis ground (

−−−−

):

Does the voltage change less than the speci-
fied value by shaking harness and connector 
of ECM while monitoring the value with voltage 
meter?

1.0 V

Repair poor con-
tact in ECM con-
nector.

Go to step 5.

5

CHECK OUTPUT SIGNAL FROM ECM.
Measure voltage between ECM connector and 
chassis ground.

Connector & terminal

(B137) No. 6 (+) — Chassis ground (

−−−−

):

Is the measured value less than the specified 
value?

1.0 V

Go to step 7.

Go to step 6.

EN(H6DO)-119

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

6

CHECK OUTPUT SIGNAL FROM ECM.
Measure voltage between ECM connector and 
chassis ground.

Connector & terminal

(B137) No. 6 (+) — Chassis ground (

−−−−

):

Does the voltage change less than the speci-
fied value by shaking harness and connector 
of ECM while monitoring the value with voltage 
meter?

1.0 V

Repair poor con-
tact in ECM con-
nector.

Go to step 7.

7

CHECK POWER SUPPLY TO FRONT OXY-
GEN (A/F) SENSOR.
1) Turn ignition switch to OFF.
2) Disconnect connector from front oxygen (A/

F) sensor.

3) Turn ignition switch to ON.
4) Measure voltage between front oxygen (A/

F) sensor connector and engine ground.

Connector & terminal

(E24) No. 2 (+) — Engine ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

10 V

Go to step 8.

Repair power sup-
ply line.

NOTE:
In this case, repair
the following:
• Open circuit in 
harness between 
main relay and 
front oxygen (A/F) 
sensor connector
• Poor contact in 
front oxygen (A/F) 
sensor connector
• Poor contact in 
main relay con-
nector

8

CHECK FRONT OXYGEN (A/F) SENSOR.
1) Turn ignition switch to OFF.
2) Measure resistance between front oxygen 

(A/F) sensor connector terminals.

Terminals

No. 2 — No. 1:

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

10 

Ω

Repair harness 
and connector.

NOTE:
In this case, repair
the following:
• Open or ground 
short circuit in har-
ness between 
front oxygen (A/F) 
sensor and ECM 
connector
• Poor contact in 
front oxygen (A/F) 
sensor connector
• Poor contact in 
ECM connector

Replace front oxy-
gen (A/F) sensor. 
<Ref. to 
FU(H6DO)-43, 
Front Oxygen (A/
F) Sensor.>

Step

Value

Yes

No

EN(H6DO)-120

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

H: DTC P0052 — HO2S HEATER CONTROL CIRCUIT HIGH (BANK 2 SENSOR 

1) —

• DTC DETECTING CONDITION:

• Immediately at fault recognition

CAUTION:
After repair or replacement of faulty parts, conduct Clear Memory Mode <Ref. to EN(H6DO)-54, OP-
ERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H6DO)-47, OPERATION, Inspec-
tion Mode.>.

EN(H6DO)-121

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

• WIRING DIAGRAM:

EN-01087

BATTERY

F44

B61

SBF-5

6

B47

MAIN RELAY

1

2

3

5

4

6

9

8

21

31

2

1

5

B252

E49

ECM

18

29

19

5

4

7

6

20

30

4

1

3

FRONT 

OXYGEN 

(A/F) 

SENSOR RH

E47

2

4

3

1

FRONT 

OXYGEN 

(A/F) 

SENSOR LH

E24

B137

E3

B22

B83

11

8

1

2

3

E2

B21

2

3

E2

B21

20

19

E49

B252

4

8

LHD

RHD

LHD

RHD

B252

B47

3

4

5

6

1

2

E24

E47

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 2 3 4
5 6 7 8

3

4

1

2

1 2 3 4
5 6 7 8

F44

B21

1 2

5

6 7

8

13

14 15

16

9 10

11 12

3 4

17 18

19 20

B83

1 2 3 4

5 6 7 8 9 10

11 12

19

20

13 14 15 16 17 18