Subaru 2002 Impreza Service Manual page 128

ON-BOARD REFUELING VAPOR RECOVERY (ORVR) SYSTEM
Emission Control
(Aux.
Emission Control Devices)
8. On-board Refueling Vapor Recovery (ORVR) System
A: GENERAL
The on-board refueling vapor recovery system allows the fuel vapors in the fuel tank to be
introduced directly into the canister through the vent valve when the fuel tank inside pressure in-
creases as a result of refueling.
The diagnosis of the system is performed by monitoring the fuel tank inside pressure data from
the fuel tank pressure sensor while forcibly closing the drain valve.
B: OPERATION
0
While driving
Since the back side of the diaphragm in the pressure control solenoid valve is open to the atmo-
sphere, the diaphragm is held pressed by the atmospheric pressure in the position where only the
external air is introduced into the canister. When the fuel vapor pressure acting on the other side
of the diaphragm increases and overcomes the atmospheric pressure, it pushes the diaphragm
and opens the port through which the fuel vapors make their way to the canister.
I I
I I
1 1 1
/
(1) Canister
(2) Pressure control solenoid valve
(3) Purge control solenoid valve
NF0471
(4) Intake manifold
(5) Shut-off valve: opened
EC-20