Patent ID: 7216639

Claim:
An abnormality diagnosis device for an air-fuel ratio sensor, comprising: diagnostic value measurement control means for, when an engine is in a predetermined operating state, measuring a diagnostic value relating to response to the air-fuel ratio sensor a plurality of times by carrying out predetermined air-fuel ratio control; abnormality determination means, for determining whether or not the air-fuel ratio sensor has an abnormality based on comparison of an average value of each of the diagnostic values and a predetermined abnormality determination value; disturbance correction value calculation means for respectively comparing each diagnostic value measured by the diagnostic value measurement control means with a correction allowable upper limit value that is set in advance to a value between an average value of each normal diagnostic value, measured in advance a plurality of times using a normal air-fuel ratio sensor, and an average value of each abnormality diagnostic value, measured in advance a plurality of times using an abnormality air-fuel ratio sensor, and, if the diagnostic value is smaller than the correction allowable upper limit value, calculating a disturbance correction value by subtracting a predetermined correction reference value from the diagnostic value, while if the diagnostic value is larger than the correction allowable upper limit value, setting the disturbance correction value to zero for the diagnostic value; and correction means for, at the time of determination by the abnormality determination means, correcting a relative relationship between an average value of the diagnostic values and the abnormality determination value based on an average value of the disturbance correction values.