air is being introduced into the canister.
Apparatuses for diagnosing a failure in the fuel vapor purge system, i.e., those for detecting leakage due to a hole(s) formed in a purge path, are also well known in the art. The purge path may include the fuel tank, fuel vapor conduit, canister, and purge passage. In many of the apparatuses, a negative pressure in the intake passage produced during operation of the internal combustion engine is introduced into the purge path through the purge passage, and then the purge path is temporarily sealed. In this condition, subsequent changes in the pressure within the purge path are measured by a pressure sensor. If the rate of increase of the pressure is higher than a predetermined value, the fuel vapor purge systemsystem comprises (1) a pressure sensor that measures a pressure of a space in the fuel tank, (2) a diagnosing unit that conducts leak diagnosis of the purge path based on a change in the pressure in the fuel tank and an amount of fuel vapor generated in the fuel tank, the change in the pressure being measured after sealing the purge path while providing a difference between inside pressure and outside pressure of the purge path, the amount of fuel vapor being measured after applying an atmospheric pressure to the purge path and sealing the purge path, and (3) a determining unit that determines that the purge path has reached an atmospheric pressure state upon detection of a predetermined state after starting application of the atmospheric pressure