Patent ID: 6983739

Claim:
An evaporative fuel control system for an internal combustion engine, comprising: a canister for absorbing evaporative fuel generated in a fuel tank, said canister being disposed on an evaporative fuel control passage that connects an intake passage of the engine with said fuel tank; an atmosphere open passage which connects said canister with the atmospheric air; a purge valve disposed between said intake passage and said canister to supply to the intake passage, for a purge control, the evaporative fuel generated in the fuel tank and absorbed by said canister; a switching valve to selectively communicate/shut said atmosphere open passage with/to the atmosphere; a reference pressure detecting means; a pressure reducing means to vacuum or reduce the pressure inside of the evaporative fuel control system; a leak diagnosis means to diagnosis leakage within the evaporative fuel control system by using a reduced pressure in the evaporative fuel control system which is reduced by said pressure reducing means when said switching valve is shifted so as to shut off the atmosphere open passage to the atmospheric air, and a reference pressure detected by said reference pressure detecting means; and a failure diagnosis means to determine whether said switching valve is in a state of failure by using a pressure variation when shifting of said switching valve for the leak diagnosis.