Genuine OEM Volkswagen Belt Tensioner, part number 06J903133D. This critical component is responsible for maintaining the correct tension on the engine's serpentine or drive belt, which powers accessories like the alternator, power steering pump, and air conditioning compressor. It ensures efficient power transfer and prevents belt slippage or excessive wear. Weighing approximately 0.73 kg, this tensioner is built for durability. Choosing a genuine OEM belt tensioner guarantees the correct spring force, bearing quality, and precise alignment, which are essential for reliable accessory operation and extended belt life.