Historically the dynamic characteristics of thermal mass air flow sensors for automotive control use have been experimentally defined by time response measurements. These simple models have not provided an accurate description of the system dynamics that can be used to predict system performance. In addition the direct measurement of the time response is a difficult experimental task and the resulting data is difficult to interpret.This paper presents a frequency domain approach to the experimental definition of the sensor dynamic response. The resulting sensor mode! is easy to implement and to interpret. It is useful both to the sensor engineer for sensor design and understanding, and to the power-train system engineer for engine control system design and analysis.