2005 Other Mercedes Benz Models Tensioner

Thats a great question. Now judging that your vehicle is an 05, I doubt the belt broke due to old age. The question is, what could have caused it to break. If the tensioner pulley were to cease, the belt would keep spinning on the froze pulley and eventully destroy itself. The tensioner is not the only thing to cause belt breakage. To test : with the belt removed and engine off, check all the pulleys and make sure the spin freely. If one pulley is stuck/ceased, that pulley/component will be need to be replaced. Possibilities could be : water pump, alt, power steering, ac compressor, ilder pulley, tensioner. Again MOST LIKELY the belt broke due to failure of something pulley related. In the case of all pulleys being checked and ok, it could just be a bad belt. Check it out and let us know what you find.