| 摘要 |
<p>PURPOSE: To enhance diagnosing accuracy by judging that a secondary air supply system is abnormal when a sensor output value does not become equal to or smaller than a preset value in a preset time after supply of secondary air is started on condition that an output value of an air-fuel ratio sensor exceeds the preset value in a condition where supply of secondary air is stopped. 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 as secondary air supply system, 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, an air fuel ratio feedback correction factor is clamped, and when a condition at secondary air supply stopping time is satisfied, secondary air is forcedly supplied. When output of an O2 sensor 26a does not become equal to or smaller than a preset value in a preset time, it is judged as abnormality of the secondary air supply system.</p> |
