Subaru Legacy IV (2008 year). Manual - part 200

GD(H4SO)-102

Diagnostic Trouble Code (DTC) Detecting Criteria

GENERAL DESCRIPTION

0.04-inch Diagnosis

Mode Table for Evaporative Emission Control System Diagnosis

Mode

Mode Description

Diagnosis Period

Mode Z

(Purge control solenoid valve 

opening failure diagnosis)

Perform purge control solenoid valve opening failure diagnosis from 
the size of tank pressure variation from diagnosis start.

0 ms + 3000 ms — 0 ms 

+ 3000 ms + 13000 ms

Mode A

(Estimated evaporation amount)

Calculate the tank pressure change amount (P1).

10000 ms

Mode B

(Sealed negative pressure, 

large leakage judgment)

Decrease the pressure in the tank to the target value by introducing 
the intake manifold pressure to the fuel tank.
If the tank pressure cannot be reduced, it is diagnosed as large leak.

0 — 10000 ms 

+ 25000 ms

Mode C

(Pressure increase check, 

advanced OK judgment)

Wait until the tank pressure returns to the target (start level of P2 
calculation). If the tank pressure does not become the value, make 
advanced OK judgment.

0 — 18500 ms

Mode D

(Negative pressure variation 

measurement, evaporation 

leakage diagnosis)

Calculate the tank pressure variation (P2), and obtain the diagnostic 
value using P1 found in Mode A.
Perform the evaporation diagnosis using the diagnostic value.

0 ms + 10000 ms

Mode

Behavior of tank internal pressure under 

normal conditions

Diagnostic item

DTC

Mode Z

Roughly the same as barometric pres-
sure (Same as 0 kPa (0 mmHg, 0 inHg))

Purge control solenoid valve is judged to 
be open.

P0457

Mode A

Pressure is in proportion to amount of 
evaporative emission.

 — 

None

Mode B

Negative pressure is formed due to 
intake manifold negative pressure

Large leak

P0457

Mode C

Reaches target pressure

 — 

None

Mode D

Pressure change is small.

EVAP system large leak determination. 
[1.0 mm (0.04 in)]

P0442

Mode

Z

Mode

A

Mode

B

Mode

C

Mode

D

OK

OK

OK

OK

OK

NG

Early OK

Large leakage judgement

Cancel

Mode

Z

Extend

NG

NG

OK

END

EN-02872

GD(H4SO)-103

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 of 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 judgment.

0 — 0 ms + 200000 ms

Mode E

(Evaporation generated amount 

calculation)

Calculate the amount of evaporation (P1).

0 — 0 ms + 200000 ms 

+ Value of 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)

21000

21000

21500

22000

22000

22000

22000

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(H4SO)-104

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(H4SO)-105

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)