Patent attributes
Concentration measurement is performed multiple times from a period in which pressure in a purge device increases due to generation of fuel vapor after operation of an engine is stopped. A concentration stabilization period, in which a change in the fuel vapor concentration is equal to or less than a reference value, is calculated based on results of the multiple times of the concentration measurement. Leak diagnosis is performed during the concentration stabilization period. As a result, even if a period for the pressure in the purge device to stabilize fluctuates due to an environment in which a vehicle is located, the leak diagnosis can be performed immediately when the pressure in the purge device stabilizes and a state suitable for the leak diagnosis is reached.
