PURPOSE: To improve accuracy of judgement by judging that an exhaust gas component concentration sensor is in an active condition when an exhaust gas component concentration detected value exceeds the first predetermined value, however the sensor is in an inactive condition when a detected value is less than the second predetermined value (< the first predetermined value).
CONSTITUTION: An engine 5 controls the air fuel ratio of mixture by letting a control circuit 20 control an air-fuel ratio control means such as a linear type electromagnetic valve 9 and the like based on the output from an O2 sensor 14 acting as an exhaust gas component concentration sensor when an air-fuel ratio feed-back control condition is satisfied. In this case, it is judged by the control circuit 20 that the O2 sensor 14 is in an active condition when an oxygen concentration detected value given by the O2 sensor 14 exceeds the first predetermined value. However, it is also judged that the O2 sensor 14 is in an inactive condition when the oxygen concentration detected value becomes lower than the second predetermined value smaller than the first predetermined value. In addition, said judgement is adapted to be formed when an engine idling is detected.
SUZUKI KOZO
KOBAYASHI HIDEO
