Exhaust gas purification system and corresponding method of diagnosing

摘要

An apparatus for an exhaust gas system includes a main exhaust passage, a main catalytic converter (4) disposed in the main exhaust passage (3), a bypass exhaust passage (7), a bypass catalytic converter (8) disposed in the bypass exhaust passage, and a valve (5) configured to open or close a section of the main exhaust passage. The bypass exhaust passage bypasses the main exhaust passage between a branch point of the bypass exhaust passage out of the main exhaust passage and a junction with the main exhaust passage at a upstream side of the main catalytic converter. A first sensor (13) indicates a first air-fuel ratio of exhaust gas in the bypass exhaust passage. A second sensor (10) indicates a second air-fuel ratio of exhaust gas flowing into the main catalytic converter. A controller determines whether the valve in the closed configuration leaks exhaust gas based on the first and second air-fuel ratios of exhaust gas.