Genuine OEM Audi Cooling System Breather Line, part number 4G0121081BH. This pipe is a critical component of the engine cooling system, specifically designed to allow trapped air to escape, preventing air pockets that can hinder cooling efficiency. It is located on the front left side of the engine bay. This lightweight line weighs 0.016 kg. Using a genuine OEM breather line ensures precise routing, correct material composition for coolant resistance, and proper sealing to maintain system pressure and prevent overheating.