| 摘要 |
<p>PURPOSE: To enhance diagnosing accuracy by judging that a secondary air supply system is abnormal when a variation between output of an air-fuel ratio sensor in a condition where secondary air is supplied and output of the air-fuel ratio sensor in a condition where supply of secondary air is stopped is smaller than a reference value. CONSTITUTION: A secondary air supply passage 32 whose inlet side is connected to an intake air system is opened in an exhaust manifold 25, and a secondary air directional control valve 33 is interposed in this passage 32. In the case of trouble diagnosing processing of such a secondary air supply system, in a CPU, when conditions such as an idle switch is turned on and a condition where car speed is lower than preset car speed passes for a preset time or more and air-fuel ratio feedback control is performed are all satisfied, a preset value is added to an air-fuel ratio feedback correction factor, and is clamped to the rich side, and a variation between respective outputs of an air-fuel ratio sensor 26a in a condition where secondary air is supplied and a condition where supply of secondary air is stopped is compared with a reference value, and when (a variation < a reference value) is realized, it is judged as abnormal.</p> |
