Diagnostic system for exhaust gas recirculation device

Claim 1

A diagnostic system of an exhaust gas recirculation device having an exhaust gas recirculation control valve which is arranged in an exhaust gas recirculation passage interconnecting an exhaust passage to an intake passage of an internal combustion engine, said diagnostic system comprising: first determining means of determining whether the engine is operating in a state at which the recirculation of exhaust gas is to be carried out; detecting means for detecting a temperature in the exhaust gas recirculation passage downstream of the exhaust gas recirculation control valve; count means having a count value which is variable between a predetermined first value and a predetermined second value in response to a result of a determination by said first determining means, said count value being changed from said first value toward said second value when the engine is operating in a state where the recirculation of exhaust is to be carried out; means for storing a first temperature detected by said detecting means when said count value is equal to said first value; and second determining means for obtaining a difference between said first temperature and second temperature detected by said detecting means when said count value becomes equal to said second value, to thereby determine that a malfunction has occurred in the exhaust gas recirculation device when said difference is lower than a predetermined value.