Leak diagnosis apparatus

A leak diagnosis apparatus for performing leak diagnosis of a fuel tank mounted on a vehicle, comprising:

• an electronic control unit including an arithmetic processing circuit and a memory, the electronic control unit being configured to:
• calculate an amount of change in a pressure in the fuel tank and an amount of change in a temperature of a fuel in the fuel tank while an ignition is turned off,
• determine whether a leak in the fuel tank is absent or present, acquire the pressure and an outside air temperature,
• estimate a plurality of change patterns of the temperature of the fuel in the fuel tank based on a change in the outside air temperature,
• specify a change pattern in which a difference between a maximum value of the temperature of the fuel in the fuel tank and a minimum value of the temperature of the fuel in the fuel tank is smallest among the plurality of change patterns, and
• calculate a difference between the maximum value of the temperature of the fuel in the fuel tank and the minimum value of the temperature of the fuel in the fuel tank in the specified change pattern as the amount of change in the temperature of the fuel in the fuel tank, wherein the electronic control unit is configured to determine that the leak in the fuel tank is absent, when the amount of change in the pressure in the fuel tank is larger than a pressure determination value, and the electronic control unit is configured to determine that the leak in the fuel tank is present, when the amount of change in the pressure in the fuel tank is equal to or smaller than the pressure determination value and when the amount of change in the temperature of the fuel in the fuel tank is larger than a temperature determination value.