| 摘要 |
<p>PURPOSE: To eliminate influence by the occurrence of a misfire or the like, and reliably detect abnormality by judging that a secondary air supply system is abnormal by comparing output values of first and second air-fuel ratio sensors and third and fourth judging values with each other in a condition where a condition at secondary air supply stopping time is satisfied and secondary air is supplied. CONSTITUTION: In an electronic control device 40, a ROM 42, an I/O interface 45 or the like are connected to each other through a bus line 46, and an FO2 sensor 26a and an RO2 sensor 26b are connected to an input port of the I/O interface 45. A failure diagnosing program or the like of a secondary air supply system is stored in the ROM 42. In this failure diagnosis, when an engine operating condition satisfies a preset condition, failure diagnosis of the secondary air supply system is started. When respective output values of first and second air-fuel ratio sensors on the upstream and downstream side of a catalyst exceed third and fourth judging values, it is judged as abnormal. Therefore, nonuniformity of the air-fuel ratio between cylinders and influence by the occurrence of a misfire are eliminated, and abnormality is reliably detected.</p> |
