Mine has quite a bit of slack.
how do I tension it or replace it.

 

Is it a separate belt than the usual serpentine one that powers everything? If it's a serpentine belt, they are usually automatically tensioned with a spring loaded tensioner. What year model is your car?

 

Mine is a A4 2004 model 1.8 Turbo diesel

 

Mine is a 2004 1.8 turbo diesel

 

Is it making noise? Squealing on acceleration and such? I'm showing nothing but serpentine belts for these cars. One belt runs the power steering, alternator, and A/C Compressor and it is tensioned by a single spring loaded tensioner. Perhaps the belt just needs replaced. The tensioners generally last a long time. The spring part anyway. Sometimes the pulleys will start to make noise when the bearings on them start to go bad. Doesn't affect the tension though.

 

Thank you for your time and effort in helping me.
I really appreciate it.
I'm going to check out the alternator as well apparently there is a clutch mechanism behind the pulley that can sieze and that causes the belt to slip and make a noise under load.
Have you heard of that before?
Once again thank you for your help.
Toni

 

Actually, I have. There's a clutch of sorts in the Alternator that prevents it from over revving, I think. Hope you get it sorted out.