The breather tube is a part of the PCV system in your vehicle. The breather tube connects the crankcase to a clean source of fresh air. Usually, clean air from the air cleaner flows into this tube and into the engine. This part is notoriously faulty in most models and nearly everybody was forced to replace it at some point in time. The early units did not have a built in check valve and commonly leaked under pressure, causing drivability issues and external oil leaks.