The main risk associated with a Fan Belt Tensioner problem in a Volkswagen is that it can cause damage to the engine. This is because the fan belt tensioner is responsible for keeping the fan belt tight and this stops it from slipping and also prevents it from coming off the pulley wheel. If the tensioner fails, the fan belt may slip off or become loose, which could lead to a whole host of issues. A slipping or loose fan belt can cause the engine to overheat, leading to serious engine damage. It can also cause the alternator to fail, which would prevent the vehicle from starting and can cause the battery to run down quickly. In some cases, a damaged fan belt tensioner can cause the vehicle to suddenly lose power while driving, which could be dangerous.