Sprinter II 2016-2018 3.0L V6 Diesel
Sprinter III 2019+ 3.0L V6 Diesel
This is the main serpentine belt tensioner. If you have rear A/C, see the secondary tensioner/damper assembly, shown below.
If you have had premature failures of this tensioner , serpentine belt, or any of the other pulleys and items driven by the belt, you most likely have a seized alternator pulley. The alternator pulley is a decoupling/declutching pulley and has a one-way clutching mechanism to minimize belt flutter. Belt flutter places stress on the entire belt drive system and the tensioner acts as a belt shock absorber. If the declutching pulley has seized, it will greatly shorten the life of the belt tensioner and often causes a pulley to break off or a fracture. Replace the alternator pulley or the alternator in order to solve this problem. To check the integrity of your alternator pulley, simply remove the belt and place a screwdriver into the front of the alternator cooling fan to stop the armature from rotating. Then turn the pulley by hand. If it moves one direction but, not the other, it is functional. If it will not rotate at all, it has failed.See this video for more info: http://www.gatesprograms.com/adp