Patent ID: 7100586

Claim:
A failure diagnosis system for an exhaust gas recirculation device provided in an internal combustion engine for recirculating a part of an exhaust gas into an intake pipe of the internal combustion engine via a recirculation valve, comprising: a detection unit that detects on state and off state actual pressures within the intake pipe, the on state and the off state actual pressures respectively being detected when the exhaust gas is recirculated and is not recirculated; a calculation unit that calculates on state and off state estimated intake pipe pressures, the on state and the off state estimated intake pipe pressures respectively being estimated pressures within the intake pipe upon detection of the on state and off state actual pressures; and a diagnosis unit that diagnoses a failure in the exhaust gas recirculation device by comparing a difference between the on state estimated intake pipe pressure and the off state estimated intake pipe pressure with a difference between the on state actual pressure and the off state actual pressure.