Your BMW has two types of factory air filters. One is for its engine. The other is for its cabin. Without an engine air filter, your engine parts would end up covered in contaminants. Without a cabin air filter, the ducts, vents, and fans in your HVAC system would end up choked with dust, pollen, and other allergens. Installing original BMW air filters is the best way to prevent both problems. However, even top-quality filters degrade over time. They can clog, or their fibers can break down. Engine air filters full of muck can lead to an over-enriched fuel-to-air ratio in your engine. As a result, your engine may lose fuel economy, put out more emissions, or just not work as well. It can even misfire. Gunky cabin air filters can negatively affect air circulation in your heater and air conditioner. As a result, these systems can malfunction. That can make it harder to get consistent interior temperatures, not to mention that it can lead to smelly interior air. It can even stress your motor. The best sign that it's time to change air filters is when their fibers become brittle, discolored, or obstructed. However, better signs include weird engine noises, excessive exhaust, bad cabin odors, and choked airflow. The best air filters for the job? Genuine BMW. They come from your OEM already the ideal fit for your car or SAV. Buy yours online from our auto parts counter today!