| 摘要 |
<P>PROBLEM TO BE SOLVED: To estimate a leakage quantity of a switching valve for opening-closing a main passage from pulsation of sensor output, by installing an exhaust flow rate sensor in a confluent part of a passage of bypassing a catalyst of an exhaust pipe and a catalyst bypass passage having the switching valve for switching the bypass passage, in this invention, for providing a diagnostic system for diagnosing leakage of a passage switching valve, since exhaust emission control performance is deteriorated, when uncontrolled exhaust emission flows out to an external part as it is in an inactive stage of a main catalyst, when passage switching by the passage switching valve is insufficient, for example, when the exhaust gas leaks though the passage switching valve for opening-closing the main passage exists in a closing position. Ž<P>SOLUTION: The leakage of the switching valve for opening-closing the main passage is diagnosed from pulsation of an exhaust flow rate sensor signal by installing the exhaust flow rate sensor in the confluence part of the bypass passage. Ž<P>COPYRIGHT: (C)2010,JPO&INPIT Ž
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