Diagnostic apparatus for engine system

A diagnostic apparatus for an engine system, the diagnostic apparatus comprising:

• an engine;
• a fuel tank that stores fuel for the engine, the fuel tank including a tank body portion in which the fuel is stored, and in which a tank internal pressure sensor is provided, a fuel introduction pipe communicating with the tank body portion, and a check valve for restricting backflow of the fuel from the tank body portion to the fuel introduction pipe while allowing introduction of the fuel from the fuel introduction pipe into the tank body portion;
• a canister that adsorbs fuel vapor generated in the fuel tank;
• a vapor passage communicating the fuel tank with the canister;
• a purge passage communicating an intake passage of the engine with the canister;
• a sealing valve that opens and closes the vapor passage;
• a purge valve that opens and closes the purge passage;
• a canister internal pressure sensor that detects canister internal pressure that is internal pressure of the canister;
• a tank internal pressure sensor that detects tank internal pressure that is internal pressure of the fuel tank;
• a decompression pump that reduces the canister internal pressure to be lower than atmospheric pressure;
• a determination unit that determines whether the tank internal pressure is no lower than the atmospheric pressure in a state in which the engine is stopped and a valve closing command is issued to the sealing valve;
• a canister leak diagnostic unit that performs leak diagnosis of the canister when an affirmative determination is made by the determination unit;
• and
• a tank leak diagnostic unit that performs leak diagnosis of the fuel tank, based on at least one of the canister internal pressure and the tank internal pressure after starting operation of the decompression pump in a state in which a valve closing command is issued to the purge valve and a valve opening command is issued to the sealing valve, when diagnosis is made that there is no leak in the canister.