They are programed by MB specific to your vin at time of purchase. Replacement keys from eBay are paperweights.

If you are referring to sych'ing, that is in your owner manual. Has also been posted here numerous times.

__________________
Terry Allison
N. Calif. & Boca Chica, Panama

09' E320 Bluetec 77k (USA)
09' Hyundai Santa Fe Diesel 48k (S.A.)