Why do I need to replace my cabin air filter? iMost car owners are aware that they need to change their car’s engine oil on a regular basis. However, many people are less familiar with the cabin air filter. This filter is responsible for cleaning the air that enters the car’s cabin, and it should be replaced at least every 12,000 miles. A clogged cabin air filter can reduce airflow and lead to a musty smell inside the car. It can also cause respiratory problems for passengers with allergies or asthma. Replacing the cabin air filter is an inexpensive task, so there’s no excuse for not keeping up with this important maintenance item.