| 摘要 |
PROBLEM TO BE SOLVED: To diagnose failure of parts with excellent accuracy, which control an exhaust emission on the basis of the detected value of an oxygen concentration sensor which detects an oxygen concentration in exhaust. SOLUTION: After an engine is started, if the detected value of an oxygen concentration sensor 17 shows an abnormal value during an idle operation period before an EGR device 21 is operated, it is diagnosed that the oxygen concentration sensor 17 is out of order. Also, the EGR device 21 is operated for a short time during an idle operation period before the EGR device 21 is operated, and the failure of the EGR device 21 is diagnosed on the basis of the variation of the detected value of the oxygen concentration sensor 17 before and after the short operation of the EGR device 21. Further, when both EGR device 21 and turbosupercharger 13 are not operated, a fuel injection amount is increased in one air cylinder (diagnostic air cylinder) being a target to diagnose its failure, and the fuel injection amount of the other air cylinder is reduced and corrected so that the increment of the fuel injection amount of the diagnostic air cylinder is canceled, then the failure of the injector 22 of the diagnostic air cylinder is diagnosed on the basis of the detected value of the oxygen concentration sensor 17 at that time. |
