The main purpose of a mass air flow sensor is to read the amount of air entering your engine. This information is used by your car's ECM to determine fuel trim and other necessary metrics in order to deliver the best performance and economy. The more air is flowing over the membrane, the higher the temperature difference between both measuring areas is rising. As this sensor ages it becomes inaccurate or simply burns out. When this happens your engine may not run properly and you will likely have a check engine light.