DIAGNOSTIC APPARATUS FOR ENGINE SYSTEM

A diagnostic apparatus for an engine system includes: a fuel tank including a tank body portion storing fuel and provided with an tank internal pressure sensor, a fuel introduction pipe communicating with the tank body portion, and a check valve for restricting the backflow of fuel from the tank body portion to the fuel introduction pipe; a determination unit for determining whether the tank internal pressure is equal to or higher than an atmospheric pressure in a state in which an engine is stopped and a valve closing command is issued to a sealing valve; a canister leak diagnosis part for performing a leak diagnosis of a canister when an affirmative determination is made in the determination part; and a tank leak diagnostic unit for performing a leak diagnosis of the fuel tank when a determination that there is no leak in the canister.