FUEL TANK SYSTEM

In a fuel tank system, a control unit diagnoses a failure of a fuel storage unit and a processing unit. The fuel storage unit includes a vapor passage through which a fuel tank and a sealing valve are communicated with each other, a first pressure detection unit, and a second pressure detection unit disposed at a position different from the first pressure detection unit. The control unit specifies a presence or an absence of a clogging of the vapor passage based on a first pressure value detected by the first pressure detection unit and a second pressure value detected by the second pressure detection unit when the pressure in the fuel tank is changed by the pressure generation unit in a condition that the sealing valve is controlled to be opened.