Abnormality detecting apparatus for fuel vapor treating system and method for controlling the apparatus

摘要

When detection of an abnormality in a fuel vapor treating system is executed, a vapor zone including a fuel tank and a canister is sealed. The sealed vapor zone is pressurized. Whether fuel vapor is leaking from the vapor zone is determined based on the pressure in the sealed vapor zone. A canister valve selectively connects a canister with and disconnects the canister from the atmosphere. During the abnormality detecting procedure, an electronic control unit (ECU) shuts the canister valve. After the abnormality detecting procedure is ended, the ECU sends a control signal having a predetermined frequency to the canister valve, thereby gradually increasing the opening size of the canister valve. Accordingly, the pressure in the vapor zone is gradually lowered to the atmospheric pressure. This prevents fuel vapor adsorbed by the canister from being released to the atmosphere.