VW Touareg serpentine belt tensioner. This original equipment quality tensioner pulley is a cast aluminum assembly. It has the spring loaded tension arm and the idler pulley integrated in one part. Typically if you begin to hear squealing or grinding noises from your engine, the pulley has gone bad. Poor belt tension can also cause your serpentine belt to slip, leading to premature belt failure. If you find that one of these parts is failing the entire assembly must be replaced.
A broken VW Touareg tensioner can damage your serpentine belt. The tensioners can lock up and cause the belts to snap, or they can get loose and cause the belts to slip and wear away. To diagnose issues like this, and how to fix them, a Bentley manual will be the best source for any trouble in your VW Touareg.