Fault diagnosis equipment and fault diagnosis method of the exhaust bypass valve

摘要

PPROBLEM TO BE SOLVED: To improve functions of a diagnosing device, including an increase of the opportunity of diagnosing. PSOLUTION: Fuel supply to an internal combustion engine 1 is controlled so that oxygen stays in a downstream catalyst 10, and an air-fuel ratio of air-fuel mixture to be burned in the internal combustion engine 1 is feedback-controlled based on composition of the exhaust in the upstream of an upstream catalyst 12. In this state, an exhaust bypass valve 9 is closed, and in such a state that composition of the exhaust on a downstream side of the upstream catalyst 12 is maintained near the theoretical air-fuel ratio, oxygen concentration of the downstream catalyst 10 when a predetermined time passes is detected. In the case wherein the oxygen concentration exceeds a predetermined rich slice level, a determination that the exhaust bypass valve is failed is done. PCOPYRIGHT: (C)2010,JPO&INPIT