FAILURE DIAGNOSTIC DEVICE FOR FUEL VAPOR TREATING DEVICE

摘要

PROBLEM TO BE SOLVED: To widen a chance for diagnosing the gas tightness of a canister even if the opening of a purge control valve is restricted to the set opening as specified when diagnostic negative pressure is introduced to the canister. SOLUTION: Fuel vapor collected in a canister 12 is purged into the air intake passage 7 of an engine 4. The amount of purged fuel is adjusted by a purge control valve 20. An electronic control device (ECU) 41 closes the purge control valve to isolate its diagnostic negative pressure only when it is determined that the opening of the purge control valve 20 is left opened for a specified period of time in order to introduce negative pressure generated in the air intake passage 7 as diagnostic negative pressure. After the introduction of negative pressure to the canister 12 is isolated, the ECU 41 is started to diagnose the gas tightness of the canister 12 based on the behavior of the internal pressure of the canister to be detected by a pressure sensor 31. In this place, when judgement is made of the set opening, the ECU delays to make judgement about the set period of time when the period of opening time deviated from the set period of opening time is considered to be within an allowable time.