Fault detection method and system for exhaust gas recirculation system

A fault detection system for an exhaust gas recirculation system having an exhaust gas recirculation passage connecting a throttle valve downstream side intake passage, which is arranged on a side downstream the position of arrangement of a throttle valve in an internal combustion engine, and an exhaust passage with each other and an exhaust gas recirculation valve inserted in said exhaust gas recirculation passage, whereby said exhaust gas recirculation valve is opened or closed to selectively recirculate exhaust gas in the exhaust passage to a side of said intake passage through said exhaust gas recirculation passage, which comprises:

• means for detecting the volume of air inducted through a throttle valve upstream side intake passage on an upstream side of said position of arrangement of said throttle valve, said inducted air volume detection means being disposed in said throttle valve upstream side intake passage;
• means for detecting the state of operation of the engine that the pressure difference between a pressure within said throttle valve downstream side intake passage and a pressure within said throttle valve upstream side intake passage is not greater than a critical pressure;
• means for opening or closing said exhaust gas recirculation valve upon detection by said engine operation state detection means of the engine operation state that the pressure difference between the pressure within said throttle valve downstream side intake passage and the pressure within the throttle valve upstream side intake passage is not greater than the critical pressure;
• and
• means for detecting that said exhaust gas recirculation system is not operating properly when a change in the output of said inducted air volume detection means between before and after the opening or closing of said exhaust gas recirculation valve has been determined to be smaller than a predetermined fault determination value.