Patent ID: 7383722

Claim:
A fuel vapor treatment system comprising: a canister configured to temporarily adsorb fuel vapor from a fuel tank; a fresh air introducing port fluidly connected to the canister to introduce fresh air into the canister with a fresh air introducing port on/off valve disposed in the fresh air introducing port to open and close the intake air introducing port of the canister; a purge line fluidly connected to the canister to send the fuel vapor adsorbed in the canister to an air intake system of an internal combustion engine by introducing fresh air into the canister through the fresh air introducing port and allowing the fresh air and fuel vapor to be drawn into the air intake system through a purge control valve disposed in the purge line; a pressure detecting device arranged and configured to detect a purge line pressure within the purge line; and a leak diagnosis control device configured and arranged to operatively control the purge control valve and the fresh air introducing port on/off valve so as to close the purge control valve and the fresh air introducing port on/off valve to close off the purge line after determining engine operation is stopped, the leak diagnosis control device including a pressure decrease rate calculating section configured to calculate a purge line pressure decreasing rate at which the purge line pressure decreases in accordance with a temperature decrease occurring after the engine is stopped; and a leak diagnosing section configured to conduct a leak determination to determine a leakage state of the purge line based on the purge line pressure decreasing rate of the purge line pressure.