The wear light comes on to advise you to check your pads, as they are near the end of their life. Typically I end up replacing all four corners at once, some people only need to replace the fronts, you'll need to check the pad depths front and rear to figure out if your pads are worn front and rear. If you're on a tight budget check out our PBR Deluxe or Mintex RedBox pads, they are a great budget friendly pad for the X5.
If I recall correctly you have an E53 3.0? If so the pads for your SAV can be found
HERE on our site!
ECS Tuning