Fuel tank system

A fuel tank system for a vehicle having an internal combustion engine, the fuel tank system comprising:

• a fuel storage unit having a sealing valve and configured to seal a fuel tank that stores fuel;
• a processing unit configured to process fuel evaporative gas in the fuel tank;
• and
• a control unit configured to diagnose a failure of the fuel storage unit and the processing unit,
• wherein the processing unit includes
• a communication passage through which the sealing valve and an intake passage of the internal combustion engine are communicated with each other,
• a first on-off valve configured to be opened and closed between the intake passage and the communication passage,
• a canister connected to the communication passage between the sealing valve and the first on-off valve and configured to adsorb fuel evaporative gas in the fuel tank,
• a second on-off valve configured to be opened and closed between the canister and the communication passage, and
• a pressure generation unit connected to the canister and configured to generate pressure, and
• wherein the control unit is configured to
• perform a first failure diagnosis of diagnosing a failure of the fuel storage unit in a state where the sealing valve is closed,
• when the fuel storage unit is diagnosed to be normal by the first failure diagnosis, perform a second failure diagnosis of diagnosing a failure of the first on-off valve and the second on-off valve by causing the pressure generation unit to generate pressure in a state where the sealing valve is closed, and
• when it is diagnosed by the second failure diagnosis that there is a possibility of closed-sticking in at least one of the first on-off valve and the second on-off valve, perform a third failure diagnosis of opening the sealing valve to specify a failure as any one of closed-sticking of the first on-off valve and closed-sticking of the second on-off valve.