We sell OEM air mass sensors, air flow meters, and HFMs (Hot Film Meter) for many BMWs. When the mass air sensor is bad you will notice your engine running out of tune. Your fuel mileage will suffer, throttle response will be poor, and you will notice a lack of power.There should be a Check Engine Light to alert you that the air sensor is having problems. However, there may not be a fault code for the air meter itself. Often times the code comes up as fuel trim or lean condition. In these cases the air sensor could be just one of a number of potential problems.We only sell air sensors from Original Equipment Manufacturers like, Bosch, VDO, and Siemens. Please note that HFMs are an electrical part and cannot be returned for refund.