To easily and accurately diagnose the leakage of exhaust gas into a path which bypasses a catalyst.
A trouble diagnosing device is provided with a bypass path which bypasses a catalyst set in mid course of an exhaust pipe, and a bypass valve closes the bypass path and opens a catalyst side when the temperature of exhaust emission is low. When the temperature of the exhaust emission is low, an air/fuel ratio feedback control is performed based on the output from a first oxygen sensor which is installed on the upstream side of the catalyst. On the other hand, second and third oxygen sensors are installed just below the catalyst and on the downstream side from the merged section of the bypass path, respectively. Then, when the ratio of the output frequency Hz2 of the second oxygen sensor to the output frequency Hz3 of the third oxygen sensor (Hz2/Hz3) is less than a prescirbed judgment level of HZBPV during the air/fuel ratio feedback control (S14), it is judged that air leaks into the bypass path side and an alarm is given (S15).
| JP6208892 | Work vehicle |
| WO/1997/025525 | REDUCING THE LIGHT-OFF TIME OF A CATALYTIC CONVERTER |
| JP3829766 | EXHAUST EMISSION CONTROL DEVICE FOR INTERNAL COMBUSTION ENGINE |
NAKADA TSUTOMU
MATSUMOTO MIKIO
TAYAMA AKIRA
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