The full version PDC for the pre-facelift E53 X5 is is (as other have stated) fairly easy to retrofit, I just finally finished doing this on my 2002 X5 3.0 d last weekend, GREAT to have.

The kit is 66 20 0 142 168. It is now NLA. No stock left in the US, but I did find a few in Spain, Portugal & Andorra (where I bought mine). You can also make it up from separate parts - just a bit more money.

Four sensors up front, four in the rear - THE only way to fly.

BMW retrofit instructions are good, but those written by Kevin Shek are even better (more practical with real pictures).