If the accessory belt is sloppy and loose in your vehicle, your generator, power steering, and AC might not work properly. Alternatively, if your belt snaps constantly, the tensioner is too tight.
With either problem, the only solution is a new tensioner. It applies the proper amount of tension to the belt to keep it tight against all of the accessory pulleys.
Recommended to be replaced any time accessory work is performed or when belts are replaced.
Expect long life and proper function for years to come.
Be sure you have the proper tools to perform your service. Many European vehicles require specialized tools for unique fasteners. Survey your upcoming service, then browse through the tool area on ECS Tuning's website to have all of those specialty tools sent to your door with your new parts.