Subaru Legacy (2005 year). Manual - part 472

EN(H6DO)(diag)-201

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK ANY OTHER DTC ON DISPLAY.

Is any other DTC displayed?

Check DTC using 
the List of Diag-
nostic Trouble 
Code (DTC). <Ref. 
to 
EN(H6DO)(diag)-
66, List of Diag-
nostic Trouble 
Code (DTC).>

Go to step 2.

2

CHECK CURRENT DATA.
1) Start the engine.
2) Read the data of intake manifold absolute 
pressure signal 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 value 53.3 kPa (400 
mmHg, 15.75 inHg) or more?

Make sure that the 
EGR valve, mani-
fold absolute pres-
sure sensor and 
throttle body are 
installed securely.

Go to step 3.

3

CHECK POWER SUPPLY OF EGR SOLE-
NOID VALVE.
1) Detach the connector from EGR solenoid 
valve.
2) Turn the ignition switch to ON.
3) Measure the voltage between EGR sole-
noid valve and engine ground.

Connector & terminal

(E18) No. 2 — Engine ground:
(E18) No. 5 — Engine ground:

Is the voltage more than 10 V? Go to step 4.

Repair the open 
circuit of harness 
between main 
relay and EGR 
solenoid valve 
connector.

4

CHECK EGR SOLENOID VALVE.
Measure the resistance between EGR sole-
noid valve terminals.

NOTE:

Make sure there is no foreign material between
EGR solenoid valve and valve seat.

Terminal

No. 1 — No. 2:
No. 3 — No. 2:
No. 4 — No. 5:
No. 6 — No. 5:

Is the resistance 20 — 30 

Ω?

Go to step 5.

Replace the EGR 
solenoid valve. 
<Ref. to 
FU(H6DO)-25, 
EGR Valve.>

5

OUTPUT SIGNAL FROM ECM
1) Turn the ignition switch to OFF.
2) Connect the connector to ECM and EGR 
solenoid valve.
3) Turn the ignition switch to ON.
4) Measure the voltage between ECM and 
chassis ground.

Connector & terminal

(B134) No. 8 (+) — Chassis ground (

−

):

(B134) No. 9 (+) — Chassis ground (

−

):

(B134) No. 10 (+) — Chassis ground (

−

):

(B134) No. 11 (+) — Chassis ground (

−

):

Is the voltage 0 — 10 V?

Repair the poor 
contact in ECM 
connector.

Go to step 6.

EN(H6DO)(diag)-202

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

BN:DTC P0420 CATALYST SYSTEM EFFICIENCY BELOW THRESHOLD 

(BANK1)

DTC DETECTING CONDITION:
Detects when malfunction occurs in 2 continuous driving cycles.
TROUBLE SYMPTOM:
• Engine stalls.
• Idle mixture is out of specifications.

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.>.

6

CHECK HARNESS BETWEEN EGR SOLE-
NOID VALVE AND ECM CONNECTOR.
1) Turn the ignition switch to OFF.
2) Detach the connector from EGR solenoid 
valve and ECM.
3) Measure the resistance of harness 
between EGR solenoid valve and ECM con-
nector.

Connector & terminal

(B134) No. 8 — (E18) No. 6:
(B134) No. 10 — (E18) No. 1:
(B134) No. 9 — (E18) No. 4:
(B134) No. 11 — (E18) No. 3:

Is the resistance less than 1 
Ω?

Go to step 7.

Repair the open 
circuit of harness 
between ECM and 
EGR solenoid 
valve connector.

7

CHECK HARNESS BETWEEN EGR SOLE-
NOID VALVE AND ECM CONNECTOR.
Measure the resistance of harness between 
EGR solenoid valve and chassis ground.

Connector & terminal

(B134) No. 8 — Chassis ground:
(B134) No. 9 — Chassis ground:
(B134) No. 10 — Chassis ground:
(B134) No. 11 — Chassis ground:

Is the resistance more than 1 
M

Ω?

Go to step 8.

Repair the short 
circuit of harness 
between main 
relay and EGR 
solenoid valve 
connector.

8

CHECK POOR CONTACT.
Check poor contact in ECM and EGR solenoid 
valve connector.

Is there poor contact in ECM or 
EGR solenoid valve connec-
tor?

Repair the poor 
contact in ECM 
and EGR solenoid 
valve connector.

Even if the mal-
function indicator 
light illuminates, 
the circuit has 
returned to a nor-
mal condition at 
this time.

Step

Check

Yes

No

EN(H6DO)(diag)-203

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

WIRING DIAGRAM:

BATTERY

SBF-5

B47

MAIN RELAY

A4

A5

A6

A7

2

52

54

B21

E2

ECM

B3

D31

D25

D24

B2

C35

4

3

1

REAR 

OXYGEN

SENSOR LH

E25

2

4

3

1

REAR 

OXYGEN 

SENSOR RH

E61

E3

B22

14

13

15

E3

B22

10

11

12

9

B83

B47

3

4

5

6

1

2

EN-03495

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

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:

16

B134

A:

B135

B:

B136

C:

B137

D:

B22

1 2 3 4
5 6 7 8
9 10 11 12

13 14 15 16

B136

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

35

C:

B137

5

6

7

8

2

1

9

4

3

10

22 23

11 12 13 14 15

24 25

26

16 17

18 19 20 21

27

28 29

30 31

D:

1 2 3 4
5 6 7 8

B83

3 4

1 2

E25

E61

E

E

5
3

: TERMINAL No. 
   RANDOM ARRANGEMENT

*

*

*

*

EN(H6DO)(diag)-204

ENGINE (DIAGNOSTICS)

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

Step

Check

Yes

No

1

CHECK FOR ANY OTHER DTC ON DIS-
PLAY.

Is any other DTC displayed?

Inspect the rele-
vant DTC using 
“List of Diagnostic 
Trouble Code 
(DTC)”. <Ref. to 
EN(H6DO)(diag)-
66, List of Diag-
nostic Trouble 
Code (DTC).>

NOTE:
In this case, it is
not necessary to
inspect DTC
P0420.

Go to step 2.

2

CHECK HARNESS BETWEEN ECM AND 
REAR OXYGEN SENSOR CONNECTOR.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from ECM and 
rear oxygen sensor.
3) Measure the resistance of harness 
between ECM and rear oxygen sensor con-
nector.

Connector & terminal

(B137) No. 24 — (E61) No. 3:
(B136) No. 35 — (E61) No. 4:
(B137) No. 25 — (E25) No. 3:
(B136) No. 35 — (E25) No. 4:

Is the resistance less than 1 
Ω?

Go to step 3.

Repair open circuit 
in harness 
between ECM and 
rear oxygen sen-
sor connector.

3

CHECK HARNESS BETWEEN REAR OXY-
GEN SENSOR AND ECM CONNECTOR.
Measure the resistance between rear oxygen 
sensor harness connector and chassis ground.

Connector & terminal

(B137) No. 31 — Chassis ground:

Is the resistance less than 1 
Ω?

Go to step 4.

Repair the open 
circuit between 
ECM and rear oxy-
gen sensor con-
nector.

4

CHECK EXHAUST SYSTEM.
Check for gas leaks or air suction caused by 
loose or dislocated nuts and bolts, and open 
hole at exhaust pipes.

NOTE:

Check the following positions.
• Between cylinder head and front exhaust 
pipe
• Between front exhaust pipe and front cata-
lytic converter
• Between front catalytic converter and rear 
catalytic converter

Is there any fault in exhaust 
system?

Repair or replace 
the exhaust sys-
tem. <Ref. to 
EX(H6DO)-2, 
General Descrip-
tion.>

Go to step 5.

5

CHECK CATALYTIC CONVERTER.

Is there damage at rear face or 
front face of front catalytic con-
verter?

Replace the cata-
lytic converter. 
<Ref. to EC(H4SO 
2.0)-3, Front Cata-
lytic Converter.>

Contact the SUB-
ARU dealer.