Patent ID: 6950742

Claim:
A failure diagnosis apparatus for diagnosing a failure of an evaporative fuel processing system which includes a fuel tank, a canister having adsorbent for adsorbing evaporative fuel generated in said fuel tank, an air passage connected to said canister and communicating said canister with the atmosphere, a first passage for connecting said canister and said fuel tank, a second passage for connecting said canister and an intake system of an internal combustion engine, a vent shut valve for opening and closing said air passage, and a purge control valve provided in said second passage, said failure diagnosis apparatus comprising: pressure detecting means for detecting a pressure in said evaporative fuel processing system; negative pressure reserving means for reserving negative pressure in said intake system during operation of said engine; engine stoppage detecting means for detecting stoppage of said engine; negative pressure introducing means for closing said purge control valve and said vent shut valve to introduce the negative pressure reserved in said negative pressure reserving means into said evaporative fuel processing system, when stoppage of said engine is detected by said engine stoppage detecting means; and determining means for determining whether or not there is a leak in said evaporative fuel processing system, based on the pressure detected by said pressure detecting means during a predetermined determination period after the negative pressure is introduced into said evaporative fuel processing system.