Patent ID: 7472582

Claim:
A leak diagnosis system for a vehicle having an internal combustion engine, the leak diagnosis system comprising: a fuel tank that receives fuel; a purge apparatus that is communicated with the fuel tank and purges fuel gas, which is generated through vaporization of the fuel in the fuel tank, into an intake air pipe of the engine; a pressure sensor that senses an internal pressure of the purge apparatus; a pump that has an adjustable pump capacity and supplies a pressure to an interior of the purge apparatus; a primary drive control means for driving the pump in a first stage at a first pumping capacity; a secondary drive control means for driving the pump in a second stage after the first stage at a second pumping capacity, which is lower than the first pumping capacity, wherein the second pumping capacity is set such that when at least one leak hole, which forms a predetermined total opening cross sectional area, exists in the purge apparatus, the driving of the pump at the second pumping capacity by the secondary drive control means substantially maintains a predetermined reference pressure in the purge apparatus; and a diagnosing means for diagnosing whether a leak hole exits in the purge apparatus based on the pressure measured with the pressure sensor in view of the predetermined reference pressure at the time of driving the pump in the second stage at the second pumping capacity by the secondary drive control means.