Subaru Legacy IV (2008 year). Manual - part 415

GD(H4DOTC)-110

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

0.02-inch Diagnosis

Mode

Mode Description

Diagnosis Period

Mode A

(0 point compensation)

When the pressure in the tank is not near 0 mmHg, wait until it 
returns to 0 point (near 0 mmHg).

0 — Value of Map 1

Mode B

(Negative pressure introduced)

Decrease the pressure in the tank to the target value by introducing 
the intake manifold pressure to the fuel tank.

0 — Value of Map 2

Mode C

(Negative pressure maintained)

Wait until the tank pressure returns to the target (start level of P2 
calculation).

0 — 20000 ms + 0  

+ Value from Map 2

Mode D

(Negative pressure change 

calculated)

Calculate the time it takes for the tank pressure to change to the 
Mode E shifting pressure. If the tank pressure does not change to 
the Mode E shifting pressure, make advanced OK judgement.

0 — 0 ms + 200000 ms

Mode E

(Evaporation generated amount 

calculation)

Calculate the amount of evaporation (P1).

0 — 0 ms + 200000 ms 

+ Value from Map 3

Map1

Fuel level (

2, US gal, Imp gal)

0

10, 2.64, 

2.2

20, 5.28, 

4.4

30, 7.93, 

6.6

40, 10.57, 

8.8

50, 13.21, 

11

60, 15.85, 

13.2

Time Needed for Diagnosis (ms)

12000

12000

11000

10000

7500

5000

5000

Map2

Fuel level (

2, US gal, Imp gal)

0

10, 2.64, 

2.2

20, 5.28, 

4.4

30, 7.93, 

6.6

40, 10.57, 

8.8

50, 13.21, 

11

60, 15.85, 

13.2

Time Needed for Diagnosis (ms)

21500

21500

22250

23000

23500

24000

24000

Map 3

Fuel level (

2, US gal, Imp gal)

0

10, 2.64, 

2.2

20, 5.28, 

4.4

30, 7.93, 

6.6

40, 10.57, 

8.8

50, 13.21, 

11

60, 15.85, 

13.2

Time Needed for Diagnosis (ms)

60000

60000

60000

60000

60000

60000

60000

EN-02871

Mode A 

Mode B

Mode C

Mode D

Mode E

Cancel

Early OK 2

Early OK 1

OK

OK

OK

OK

Cancel

Cancel

Cancel

Cancel

END

GD(H4DOTC)-111

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

2. COMPONENT DESCRIPTION

Pressure control solenoid valve

PCV controls the fuel tank pressure to be equal to the atmospheric air pressure. Normally, the solenoid is set
to OFF. The valve opens and closes mechanically in accordance with the pressure difference between tank
and atmospheric air, or tank and canister.
The valve is forcibly opened by setting the solenoid to ON at the time of diagnosis.

(a)

Barometric pressure

(b)

Fuel tank

(c)

Canister

(1)

Solenoid

(3)

Valve

(4)

Spring

(2)

Diaphragm

EN-01715

(a)

(b)

(c)

(4)

(1)

(2)

(3)

GD(H4DOTC)-112

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

Valve Operation and Air Flow

In the figure below, divided by the diaphragm, the part above X is charged with atmospheric air pressure, and
the part below X is charged with tank pressure. Also, the part above Y is charged with tank pressure, and the
part below Y is charged with canister pressure.
If the atmospheric air pressure port is A, tank pressure port is B, and canister pressure port is C, the air flows
according to pressure difference from each port as shown in the table below.

When A < B (solenoid OFF)

(a)

Barometric pressure

(b)

Fuel tank

(c)

Canister

Condition of pressure

Flow

A < B (solenoid OFF)

B 

o C

B < C (solenoid OFF)

C 

o B

Solenoid ON

B 

m o C

(a)

Barometric pressure

(b)

Fuel tank

(c)

Canister

EN-01716

A

B

C

X

X

Y

(a)

(b)

(c)

EN-01717

A

B

C

(a)

(b)

(c)

GD(H4DOTC)-113

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

When B < C (solenoid OFF)

When Solenoid is ON

(a)

Barometric pressure

(b)

Fuel tank

(c)

Canister

(1)

Valve

(a)

Barometric pressure

(b)

Fuel tank

(c)

Canister

EN-01718

A

B

C

(a)

(b)

(c)

(1)

EN-01719

A

B

C

(a)

(b)

(c)