Subaru Legacy III (2000-2003 year). Manual - part 326

EN(H6DO)-106

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK OUTPUT SIGNAL FROM ECM.
1) Turn ignition switch to ON.
2) Measure voltage between ECM connector 

and chassis ground.

Connector & terminal

(B137) No. 4 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the spec-
ified value?

8 V

Go to step 3.

Go to step 2.

2

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

Connector & terminal

(B137) No. 5 (+) — Chassis ground (

−−−−

):

Does the measured value exceed the specified 
value?

8 V

Go to step 3.

Go to step 4.

3

CHECK FRONT OXYGEN (A/F) SENSOR 
HEATER CURRENT.
1) Turn ignition switch to OFF.
2) Repair battery short circuit in harness 

between ECM and front oxygen (A/F) sen-
sor connector.

3) Turn ignition switch to ON.
4) Read data of front oxygen (A/F) 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(H6DO)-34, Subaru Select Moni-
tor.>
• OBD-II general scan tool
For detailed operation procedure, refer to the 
OBD-II General Scan Tool Instruction Manual.

2.3 A

Replace ECM. 
<Ref. to 
FU(H6DO)-46, 
Engine Control 
Module.>

END

4

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

Connector & terminal

(B137) No. 4 (+) — Chassis ground (

−−−−

):

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

8 V

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

Go to step 5.

5

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

Connector & terminal

(B137) No. 5 (+) — Chassis ground (

−−−−

):

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

8 V

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

END

EN(H6DO)-107

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

MEMO:

EN(H6DO)-108

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

D: DTC P0037 — HO2S HEATER CONTROL CIRCUIT LOW (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(H6DO)-54, OP-
ERATION, Clear Memory Mode.>  and Inspection Mode <Ref. to EN(H6DO)-47, OPERATION, Inspec-
tion Mode.>.
• WIRING DIAGRAM:

EN-01088

BATTERY

F44

B61

6

T5

B19

B47

MAIN RELAY

2
1

3

5

4

6

F44

1 2 3 4
5 6 7 8

C13

B17

B19
B26

D21

D31

D9

D8

REAR 

OXYGEN 

SENSOR

5

3

6
4

1

3

4

2

1

5

B252

B83

B19

T5

T6

E49

B47

T6

B136

C:

D:

B135

B:

3

4

5

6

1

2

5

7

ECM

B135

B:

B136

C:

B137

D:

3

4

1

2

1 2

7

8 9

5

6

3

4

10 11 12
19 20 21

13 14 15 16

17 18

22 23 24

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

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

RHD

LHD

LHD

RHD

B252

1 2 3 4
5 6 7 8

B19

4

1 2 3

6

5

2

B83

1 2 3 4

5 6 7 8 9 10

11 12

19

20

13 14 15 16 17 18

EN(H6DO)-109

ENGINE (DIAGNOSTICS)

DIAGNOSTIC PROCEDURE WITH DIAGNOSTIC TROUBLE CODE (DTC)

Step

Value

Yes

No

1

CHECK GROUND CIRCUIT OF ECM.
1) Turn ignition switch to OFF.
2) Disconnect ECM connector.
3) 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 speci-
fied 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 rear oxygen 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 connector.

NOTE:
In this case, repair
the following:
• Poor contact in 
rear oxygen sen-
sor connector
• Poor contact in 
rear oxygen sen-
sor connecting 
harness 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

(B136) No. 13 (+) — Chassis ground (

−−−−

):

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

1.0 V

Go to step 6.

Go to step 4.

4

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

Connector & terminal

(B136) No. 13 (+) — 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.
1) Turn ignition switch to OFF.
2) Disconnect connector from rear oxygen 

sensor.

3) Measure voltage between ECM connector 

and chassis ground.

Connector & terminal

(B136) No. 13 (+) — Chassis ground (

−−−−

):

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

1.0 V

Contact SUARU 
distributor service.

NOTE:
Inspection by DTM
is required, be-
cause probable
cause is deteriora-
tion of multiple
parts.

Repair battery 
short circuit in har-
ness between 
ECM and rear oxy-
gen sensor con-
nector. After 
repair, replace 
ECM. <Ref. to 
FU(H6DO)-46, 
Engine Control 
Module.>