| 摘要 |
A diagnostic apparatus for use in an exhaust system of an internal combustion engine is disclosed. The system has a catalyst for purifying the exhaust gas in the exhaust gas passage and an oxygen sensor for detecting an air-fuel ratio in a combustion chamber, wherein fuel injection volume is controlled for optimizing the air-fuel ratio and the catalyst activation when the engine is operated under normal conditions, and wherein secondary air is supplied to the exhaust gas passage from a secondary air supply mechanism for forcibly adjusting the air-fuel ratio when the engine is operating under extreme conditions. The apparatus has a computing device which computes an actual volume of the secondary air supplied to the exhaust gas passage from the secondary air supply mechanism. The apparatus further has a storing device which stores data indicative of malfuncting secondary air supply mechanism members corresponding to the computed volume supplied to the exhausted gas passage, and a determining device for determining the malfunctioning member in accordance with the value detected by the oxygen sensor and the stored data corresponding the detected value.
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