| 摘要 |
PROBLEM TO BE SOLVED: To accurately diagnose deterioration of a catalyst by restraining the effects of the change of a sensor due to aging, and to enable diagnosis in the operating range to be affected greatly by exhaust gas. SOLUTION: When diagnosis of deterioration of a catalyst is not yet finished and when the diagnosing condition is established and also the diagnosis stopping conditions are not established, the difference between the output voltage THCAT of a rear exhaust temperature sensor and the output voltage THFCAT of a front exhaust temperature sensor is calculated (S1 to S4), the output voltage difference THDCAT is compared with a judging threshold CATNG which corresponds to heat of reaction by the purifying action of a normal catalyst, and deterioration of the catalyst is judged (S5). Therefore, deterioration of the catalyst can be diagnosed surely and precisely, without being affected by a change of the sensor due to aging and the responsiveness, even in an operating range which is greatly affected by exhaust gas. |
