Your Hummer air filter is an important part of its intake system. The air filters job is to help the engine breathe. All the air that flows through the engine comes through the air filter first. Without an air filter, your engine would not be able to keep out dirt, debris, and other foreign particles. Not keeping up on the cleanliness of your air filter can result in lose of performance from your vehicle. Gas mileage, emissions, and spark plug ignition can all be affected by a dirty air filter. You should plan on changing your air filter once a year. Many people change their air filters b y themselves, however you can have yours changed during an oil change or your annual tune up. If you live in an area that uses dirt roads or an area that's prone to heavy pollution, you may need to change your air filter more frequently than once a year.