Genuine OEM Audi Belt Tensioner, part number 0P2903133B. This component applies tension to the serpentine belt to ensure proper operation of accessory components like the alternator and A/C compressor. It is located in the engine's accessory drive system. Made from durable materials for long service life. Genuine OEM belt tensioners are precisely calibrated to maintain optimal belt tension, preventing slippage and premature wear.