Genuine OEM Audi Reservoir Breather Line, part number 4G0121081BB. This hose allows air to escape from a fluid reservoir, preventing pressure buildup and ensuring proper system operation. It is typically located at the rear left of the cooling system assembly. Weighing only 0.014 kg and measuring 0.18 m in length, this genuine OEM part ensures precise fitment and material integrity for reliable, leak-free performance within the cooling system.