Image Number 2 for United States Patent #4870941.
An automotive vehicle is equipped with an exhaust gas recirculation system in which a part of exhaust gas is recirculated back to the combustion chambers of the engine. The exhaust gas recirculation system is comprised of an EGR passage through which the exhaust gas flows. An EGR valve is disposed in the EGR passage to control the amount of the recirculated exhaust gas. A temperature sensor is disposed in the EGR passage upstream of the EGR valve to detect the temperature of the recirculated exhaust gas flowing through the EGR passage and output a signal representing the exhaust gas temperature. The signal is input to a control unit which is arranged to cause a warning lamp to light when the exhaust gas temperature detected by the temperature sensor is below a predetermined level, thus achieving diagnosis of abnormality in the exhaust gas recirculation system such as clogging of the EGR passage and failed operation of the EGR valve while preventing thermal damage of the temperature sensor.