Patent ID: 7036359

Claim:
A failure diagnostic system for a fuel vapor processing apparatus which is disposed correspondingly to an engine mounted on a vehicle and wherein fuel vapor generated in a fuel tank is trapped by a canister and the trapped fuel vapor is purged to an intake passage in the engine, wherein the fuel vapor processing apparatus comprises a processing flow path extending from the fuel tank to the intake passage and including the canister; and the failure diagnostic system comprises: closure means for closing the processing flow path; pressurizing means for pressurizing the interior of the processing flow path; pressure reducing means for reducing the internal pressure of the processing flow path; pressure detecting means for detecting an internal pressure of the processing flow path; temperature detecting means for detecting an atmosphere temperature of the fuel tank; first diagnostic means which, after stop of the engine, controls the closure means to close the processing flow path and which, when the atmosphere temperature detected by the temperature detecting means is lower than a predetermined value, controls the pressure reducing means to reduce the internal pressure of the processing flow path and checks air-tightness of the processing flow path based on behavior of the pressure detected by the pressure detecting means after the pressure reduction; and second diagnostic means which, after stop of the engine, controls the closure means to close the processing flow path and which, when the atmosphere temperature detected by the temperature detecting means is higher than a predetermined value, controls the pressurizing means to pressurize the interior of the processing flow path and checks the air-tightness of the processing flow path based on behavior of the pressure detected by the pressure detecting means after the pressurization.