A motor vehicle vision system (10) including a stereo imaging system (11) and a data processing device (14) establishing an object detector (15) to detect an object and a tracker (16). The data processing device (14) calculates a size related value and a disparity related value for the object. An analysis section (20) performs an analysis on a group of at least five data points corresponding to different times, each data point includes a size related value and a disparity related value. The analysis uses predetermined regression function having at least one variable, and yields a best value for each variable corresponding to a best match of the regression function to the data points. The analysis section (20) calculates from a best value a systematic error in the disparity related values and/or in the size related values.