All About Air Filters: Your vehicle's air filters are inexpensive, yet vitally important in keeping contaminants out of your engine and cabin. A typical air filter, or "engine" filter, helps keep your vehicle running at optimum performance, reduces emissions, and even helps with fuel efficiency. Under normal conditions, it is recommended to replace these filters about every 15,000 miles. A cabin air filter, on the other hand, provides most of these same benefits, but to YOU: the occupant of the vehicle. Keeping the air in your interior healthy and clean, a cabin air filter needs replacement roughly half as much as an engine filter, or about every 30,000 miles. Please note that consistent driving in smog-heavy, pollen-laden, or dirtier environments, will necessitate more frequent filter replacement.