A couple of questions.
- Does a 2004 Chevy Malibu have a cabin air filter?
- If so, where would it be located?
- How often should a cabin air filter be changed?
Some quick searching is turning up a lot of confusing info. You may have one that came with the vehicle from the factory, but it might not be in any parts database as a part you can order / purchase. You might also just have an empty spot where you could fit a filter. Here's a thread from chevymalibuforum.com..