SELF DIAGNOSTIC DEVICE IN SECONDARY AIR FEED DEVICE OF INTERNAL COMBUSTION ENGINE

摘要

PURPOSE:To easily diagnose the failure of a secondary air feed device and avoid the inconvenience by an excessive or deficient supply of secondary air. CONSTITUTION:When the feedback control of air-fuel ratio of the mixed air sucked into an engine 1 is cramped, it is judged whether the ratio is contained in a determined diagnostic operating area or not (S7). When it is within the diagnostic operation area, the supply 21 of secondary air is forcedly interrupted and continued (S10), and the change of the detection result by an oxygen sensor 16 provided on the lower stream side from the feed position of secondary air is judged (S11). When the oxygen concentration in exhaust air does not show the corresponding change at the time of interrupting and continuing the supply of secondary air, a failure of secondary air feed devices 18-23 is diagnosed.