Subaru Legacy III (2000-2003 year). Service manual — part 324

EN(H6DO)-98

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
1) Start engine, and warm-up the engine.
2) Turn ignition switch to OFF.
3) Disconnect connectors from ECM and front

oxygen (A/F) sensor.

4) Measure resistance of harness between

ECM and front oxygen (A/F) sensor con-
nector.

Connector & terminal

(B137) No. 4 — (E47) No. 1:
(B137) No. 5 — (E47) No. 1:

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

1

Ω

Go to step 2.

Repair open circuit
in harness
between ECM and
front oxygen (A/F)
sensor connector.

2

CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
Measure resistance of harness between ECM
and front oxygen (A/F) sensor connector.

Connector & terminal

(B137) No. 19 — (E47) No. 4:

Is the measured value less than the specified
value?

1

Ω

Go to step 3.

Repair open circuit
in harness
between ECM and
front oxygen (A/F)
sensor connector.

3

CHECK HARNESS BETWEEN ECM AND
FRONT OXYGEN (A/F) SENSOR CONNEC-
TOR.
Measure resistance of harness between ECM
and front oxygen (A/F) sensor connector.

Connector & terminal

(B137) No. 29 — (E47) No. 3:

Is the measured value less than the specified
value?

1

Ω

Go to step 4.

Repair open circuit
in harness
between ECM and
front oxygen (A/F)
sensor connector.

4

CHECK FRONT OXYGEN (A/F) SENSOR.
Measure resistance between front oxygen (A/
F) sensor connector terminals.

Terminals

No. 2 — No. 1:

Is the measured value less than the specified
value?

5

Ω

Go to step 5.

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

5

CHECK POOR CONTACT.
Check poor contact in ECM and front oxygen
(A/F) sensor connector.
Is there poor contact in ECM or front oxygen
(A/F) sensor connector?

There is poor contact.

Repair poor con-
tact in ECM or
front oxygen (A/F)
sensor connector.

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

EN(H6DO)-99

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

MEMO:

EN(H6DO)-100

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

B: DTC P0031 — HO2S HEATER CONTROL CIRCUIT LOW (BANK 1 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)-101

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