Genuine OEM Audi Expansion Tank Breather Line, part number 4H0121081AH. This hose is designed to allow air to escape from the cooling system's expansion tank, ensuring proper pressure regulation and preventing air pockets that can hinder cooling efficiency. It is located at the left rear of the engine bay, connected to the expansion tank. Weighing approximately 0.019 kg, this line is made from durable, heat-resistant material. Choosing genuine OEM ensures the correct routing, flexibility, and resistance to coolant for reliable cooling system operation.