ABNORMALITY DIAGNOSTIC DEVICE FOR SECONDARY AIR SUPPLY SYSTEM

Japanese Patent JP3757735

B2

PROBLEM TO BE SOLVED: To provide an abnormality diagnostic device for a secondary air supply system capable of precisely diagnosing working abnormality in simple constitution and which uses an air injection method. SOLUTION: This secondary air supply system is constituted by furnishing an air pump 13 to supply secondary air to an exhaust passage 10 of an engine 1 and a valve 12 interposed between the air pump 13 and the exhaust passage 10 and to open and close a secondary air supply passage 11. It is diagnosed that the air pump 13 has working abnormality when the valve 12 is temporarily controlled to open under a condition that a working stop command is given to the air pump 13 and a lean state of more than a specified period is detected by an air-fuel ratio sensor 15 in this opening control period.