Subaru Legacy III (2000-2003 year). Manual - part 504

EN(H4DOSTC)-186

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

AT: DTC P1131 — O2 SENSOR CIRCUIT (SHORT) (BANK1 SENSOR1) —

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-00933

BATTERY

MAIN  RELAY

SBF-5

B47

1

2

3

5

4

6

E

E

E3

3

8

9

4

5

19

29

18

ECM

B137

B22

2

4

1

3

B18

FRONT OXYGEN
(A/F) SENSOR

3 4

1 2

3

4

1

2

5

6

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

B22

B47

B18

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

EN(H4DOSTC)-187

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) Turn the ignition switch to OFF.
2) Disconnect the connector from ECM.
3) Measure the resistance of harness 

between ECM connector and chassis 
ground.

Connector & terminal

(B137) No. 19 — Chassis ground:

Does the measured value exceed the spec-
ified value?

1 M

Ω

Go to step 2.

Repair the ground 
short circuit in har-
ness between 
ECM and front 
oxygen (A/F) sen-
sor connector.

2

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

Connector & terminal

(B137) No. 29 — Chassis ground:

Does the measured value exceed the specified 
value?

1 M

Ω

Go to step 3.

Repair the ground 
short circuit in har-
ness between 
ECM and front 
oxygen (A/F) sen-
sor connector.

3

CHECK OUTPUT SIGNAL FOR ECM.
1) Connect the connector to ECM.
2) Turn the ignition switch to ON.
3) Measure the voltage between ECM con-

nector and chassis ground.

Connector & terminal

(B137) No. 19 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

4.5 V

Go to step 4.

Go to step 5.

4

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

Connector & terminal

(B137) No. 19 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the specified 
value?

10 V

Repair the battery 
short circuit in har-
ness between 
ECM and front 
oxygen (A/F) sen-
sor connector. 
After repair, 
replace the ECM.  
<Ref. to 
FU(H4DOSTC)-
40, Engine Con-
trol Module.>

Repair the poor 
contact in ECM 
connector.

5

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

Connector & terminal

(B137) No. 29 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the specified 
value?

4.95 V

Go to step 6.

Replace the front 
oxygen (A/F) sen-
sor.  <Ref. to 
FU(H4DOSTC)-
38, Front Oxygen 
(A/F) Sensor.>

EN(H4DOSTC)-188

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

6

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

Connector & terminal

(B137) No. 29 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the specified 
value?

10 V

Repair the battery 
short circuit in har-
ness between 
ECM and front 
oxygen (A/F) sen-
sor connector. 
After repair, 
replace the ECM.  
<Ref. to 
FU(H4DOSTC)-
40, Engine Con-
trol Module.>

Repair the poor 
contact in ECM 
connector.

Step

Value

Yes

No

EN(H4DOSTC)-189

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

MEMO: