Subaru Legacy (2005 year). Service manual - part 445

EN(H6DO)(diag)-93

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK POWER SUPPLY TO FRONT OXY-
GEN (A/F) SENSOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connector from front oxygen 
(A/F) sensor.
3) Turn the ignition switch to ON.
4) Measure the voltage between front oxygen 
(A/F) sensor connector and engine ground.

Connector & terminal

(E24) No. 2 (+) — Engine ground (

−

):

Is the voltage more than 10 V? Go to step 2.

Repair the power 
supply line.

NOTE:
In this case, repair
the following:
• Open circuit of 
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 connec-
tor

2

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

Connector & terminal

(B134) No. 4 — Chassis ground:
(B134) No. 5 — Chassis ground:
(B134) No. 6 — Chassis ground:
(B134) No. 7 — Chassis ground:

Is the resistance less than 5 
Ω?

Go to step 3.

Repair the har-
ness and connec-
tor.

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

3

CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of front oxygen (A/F) sensor 
heater current using Subaru Select Monitor or 
general scan tool.

NOTE:

• Subaru Select Monitor
For detailed operation procedure, refer to 
“READ CURRENT DATA FOR ENGINE”. <Ref. 
to EN(H6DO)(diag)-26, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the current more than 0.2 A? Repair the poor 

contact in connec-
tor.

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

Go to step 4.

4

CHECK OUTPUT SIGNAL FROM ECM.
1) Start and idle the engine.
2) Measure the voltage between ECM con-
nector and chassis ground.

Connector & terminal

(B134) No. 1 (+) — Chassis ground (

−

):

(B135) No. 7 (+) — Chassis ground (

−

):

Is the voltage less than 1 V?

Go to step 6.

Go to step 5.

5

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

Connector & terminal

(B134) No. 1 (+) — Chassis ground (

−

):

(B135) No. 7 (+) — Chassis ground (

−

):

Does the voltage change by 
shaking the ECM harness and 
connector while monitoring the 
value of voltage meter?

Repair the poor 
contact in ECM 
connector.

Go to step 6.

EN(H6DO)(diag)-94

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

6

CHECK FRONT OXYGEN (A/F) SENSOR.
1) Turn the ignition switch to OFF.
2) Measure the resistance between front oxy-
gen (A/F) sensor connector terminals.

Terminal

No. 2 — No. 1:

Is the resistance less than 10 
Ω?

Repair the har-
ness and connec-
tor.

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

Replace the front 
oxygen (A/F) sen-
sor. <Ref. to 
FU(H6DO)-30, 
Front Oxygen (A/
F) Sensor.>

Step

Check

Yes

No

EN(H6DO)(diag)-95

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

L: 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)(diag)-41, 
OPERATION, Clear Memory Mode.> and Inspection Mode <Ref. to EN(H6DO)(diag)-34, PROCEDURE, 
Inspection Mode.>.
WIRING DIAGRAM:

BATTERY

SBF-5

B47

MAIN RELAY

A4

A5

A6

A7

2

52

54

B21

E2

ECM

A34

A27

B7

A1

A2

A3

A26

A33

4

1

3

FRONT 

OXYGEN 

(A/F) 

SENSOR LH

E24

2

B135

B:

B134

A:

4

3

1

FRONT 

OXYGEN 

(A/F) 

SENSOR RH

E47

E3

B22

8

5

6

E3

B22

2

1

3

4

B47

3

4

5

6

1

2

A25

B22

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

3 4

1 2

E47

E24

B135

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

29 30 31

32 33

34 35

B:

B134

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

33 34

29

32

30 31

A:

B21

1 2 3 4

12 13 14 15

5 6 7 8

16 17 18 19

9 10 11

20 21 22

23 24 25 26 27 28 29 30 31 32 33

35

34

37

36

39

38

41

40

43

42

44

45

47

46

49

48

51

50

53

52

54

E

E

EN-03494

B135

B:

B134

A:

7

5
3

EN(H6DO)(diag)-96

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK OUTPUT SIGNAL FROM ECM.
1) Turn the ignition switch to ON.
2) Measure the voltage between ECM con-
nector and chassis ground.

Connector & terminal

(B134) No. 1 (+) — Chassis ground (

−

):

(B135) No. 7 (+) — Chassis ground (

−

):

Is the voltage more than 8 V?

Go to step 2.

Go to step 3.

2

CHECK FRONT OXYGEN (A/F) SENSOR 
HEATER CURRENT.
1) Turn the ignition switch to OFF.
2) Repair the battery short circuit of harness 
between ECM and front oxygen (A/F) sensor 
connector.
3) Turn the ignition switch to ON.
4) Read the data of front oxygen (A/F) sensor 
heater current using Subaru Select Monitor or 
general scan tool.

NOTE:

• Subaru Select Monitor
For detailed operation procedure, refer to 
“READ CURRENT DATA FOR ENGINE”. <Ref. 
to EN(H6DO)(diag)-26, Subaru Select Moni-
tor.>
• General scan tool
For detailed operation procedure, refer to the 
general scan tool operation manual.

Is the current more than 2.3 A? Replace the ECM. 

<Ref. to 
FU(H6DO)-34, 
Engine Control 
Module (ECM).>

Finish the diagno-
sis.

3

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

Connector & terminal

(B134) No. 1 (+) — Chassis ground (

−

):

(B135) No. 7 (+) — Chassis ground (

−

):

Does the voltage change by 
shaking the ECM harness and 
connector?

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

Finish the diagno-
sis.