Methods and system for controlling air-fuel ratios in an internal combustion engine are disclosed. One embodiment comprises, adjusting a sensor calibration correction value of an exhaust sensor upstream of a catalyst based on an exhaust sensor downstream of the catalyst. The adjustment of the sensor calibration correction value takes advantage of the fact that certain aromatic hydrocarbons causing errors in the reading of the upstream sensor are not present at the downstream sensor due to sufficient catalytic activity of a catalyst positioned between the sensors.