Patent ID: 7568476

Claim:
An air-fuel ratio control system for an internal combustion engine, including an air-fuel ratio sensor which detects an air-fuel ratio of exhaust gas in an exhaust passage of the internal combustion engine, and controlling the air-fuel ratio (feed air-fuel ratio) which is supplied to the internal combustion engine based on an output of the air-fuel ratio sensor, the air-fuel ratio control system comprising: an output-characteristics detection means for detecting output-characteristics data showing output characteristics of the air-fuel ratio sensor; and a sensor output correction means for correcting the output of the air-fuel ratio sensor or a detected air-fuel ratio based on the output-characteristics data detected by the output-characteristics detection means, wherein the output-characteristics detection means changes the feed air-fuel ratio to rich/lean, and detects the output-characteristics data by comparing a variation width of rich/lean with a quantity of an output change in the air-fuel ratio sensor.