Patent ID: 6968732

Claim:
A failure diagnostic device of an evaporative gas purge control system, comprising: an evaporative gas passage to communicate a fuel tank with a canister to adsorb an evaporative fuel generated in the fuel tank; a purge passage to communicate the canister with an engine intake system; a pressure control valve interposed in the evaporative gas passage and opened at a valve opening according to a pressure difference between the pressure in the fuel tank and a reference pressure if the pressure in the fuel tank is higher than the reference pressure; a reference pressure chamber to set the reference pressure of the pressure control valve connected to the canister; purge control means interposed in the purge passage to control an opening and a closing of the purge passage; a drain valve to open and close a fresh air introducing port opened in the canister; and tank internal pressure detecting means to detect the pressure in the fuel tank; diagnosis start means to detect that the drain valve is opened from an energized state to the drain valve, and open the purge control means; and failure determination means to compare the pressure in the fuel tank detected by the tank internal pressure detecting means with a closed sticking determination pressure of the drain valve, and to determine a closed sticking of the drain valve if the pressure in the fuel tank is lower than the closed sticking determination pressure of the drain valve.