The newer model features adaptive braking taillights. It has an extra bulb that illuminates under hard braking. Otherwise they are almost identical. If you park an '00-'03 X5 next to an '04-06' X5, you wouldn't see the differences in the taillights unless you were specifically looking for them. The lens of the new light is a little bit of a brighter red and perhaps a little clearer in the clear portion, otherwise they look identical.