Genuine OEM Volkswagen Reservoir A Reduction Agent, part number 3Q0131877H. This reservoir is designed to hold the reduction agent, commonly known as AdBlue, which is used in the selective catalytic reduction (SCR) system to reduce NOx emissions. It is an integral part of the vehicle's emissions and exhaust system. The reservoir assembly weighs approximately 6.663 kg. Genuine OEM reservoirs are constructed from materials specifically chosen for compatibility with AdBlue and to prevent leaks, ensuring the longevity and effectiveness of the emissions control system.