Subaru Legacy IV (2008 year). Manual - part 150

EN(H4SO)(diag)-203

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

BH:DTC P0448 EVAPORATIVE EMISSION CONTROL SYSTEM VENT CONTROL 

CIRCUIT SHORTED

DTC DETECTING CONDITION:
• Immediately at fault recognition
• GENERAL DESCRIPTION <Ref. to GD(H4SO)-119, DTC P0448 EVAPORATIVE EMISSION CONTROL
SYSTEM VENT CONTROL CIRCUIT SHORTED, Diagnostic Trouble Code (DTC) Detecting Criteria.>

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4SO)(diag)-50,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4SO)(diag)-41, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:

EN-06841

16

10 11 12 13 14 15

25

24

30

9

8

7

17 18 19 20
28

21 22 23

29

32

31

1

2

3

4

5

6

27

26

33 34 35

B136

17

B97

R1

1

2

7

R144

R15

R213

R46

R67

ECM

B136

SBF-7

5
3

6
4

2
1

B47

6

1

E

DRAIN
VALVE

MAIN RELAY

BATTERY

B47

3

4

1

2

5

6

1 2

3

4 5 6 7 8

1

2

3 4 5 6

R67

R213

B97

14

1 2 3 4

5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20

1 2

R144

EN(H4SO)(diag)-204

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK HARNESS BETWEEN ECM AND 
DRAIN VALVE.
1) Turn the ignition switch to OFF.
2) Disconnect the connectors from the ECM 
and drain valve.
3) Turn the ignition switch to ON.
4) Measure the voltage between ECM and 
chassis ground.

Connector & terminal

(B136) No. 17 (+) — Chassis ground (–):

Is the voltage 10 V or more?

Repair the short 
circuit to the power 
supply in the har-
ness between the 
ECM and drain 
valve connector.

Go to step 2.

2

CHECK DRAIN VALVE.
1) Turn the ignition switch to OFF.
2) Measure the resistance between drain valve 
terminals.

Terminals

No. 1 — No. 2:

Is the resistance less than 1 

:? Replace the drain 

valve. <Ref. to 
EC(H4SO)-16, 
Drain Valve.>

Repair the poor 
contact of ECM 
connector.

EN(H4SO)(diag)-205

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

BI: DTC P0451 EVAPORATIVE EMISSION CONTROL SYSTEM PRESSURE 

SENSOR

DTC DETECTING CONDITION:
• Two consecutive driving cycles with fault
• GENERAL DESCRIPTION <Ref. to GD(H4SO)-121, DTC P0451 EVAPORATIVE EMISSION CONTROL
SYSTEM PRESSURE SENSOR, Diagnostic Trouble Code (DTC) Detecting Criteria.>

CAUTION:
After repair or replacement of faulty parts, perform Clear Memory Mode <Ref. to EN(H4SO)(diag)-50,
OPERATION, Clear Memory Mode.>, and Inspection Mode <Ref. to EN(H4SO)(diag)-41, PROCEDURE,
Inspection Mode.>.
WIRING DIAGRAM:

EN-05047

6

17

13

B97

R1

7

6

4

R15

R213

3

2

1

R47

B83

B135 ECM

B97

B83

3 4

5 6

1 2

7 8

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

*

*

*

R47

1 2 3

R213

1 2

3

4 5 6 7 8

22

32

30

1 2 3 4

5 6 7 8 9

10 11 12 13 14 15 16 17 18 19 20

FUEL TANK 
PRESSURE

SENSOR

 : TERMINAL No. OPTIONAL 

ARRANGEMENT

EN(H4SO)(diag)-206

Diagnostic Procedure with Diagnostic Trouble Code (DTC)

ENGINE (DIAGNOSTICS)

Step

Check

Yes

No

1

CHECK FUEL FILLER CAP.
1) Turn the ignition switch to OFF.
2) Open the fuel flap.

Is the fuel filler cap tightened 
securely?

Go to step 2.

Tighten fuel filler 
cap securely.

2

CHECK PRESSURE VACUUM LINE.

NOTE:
Check the following items.
• Disconnection, leakage and clogging of the
vacuum hoses and pipes between fuel tank
pressure sensor and fuel tank
• Disconnection, leakage and clogging of the
air ventilation hoses and pipes between fuel fill-
er pipe and fuel tank

Is there any fault in pressure/
vacuum line?

Repair or replace 
the hoses and 
pipes.

Replace the fuel 
tank pressure sen-
sor. <Ref. to 
EC(H4SO)-12,
Fuel Tank Pres-
sure Sensor.>