can i use '05 smart key on an '08?

Unlikely. From what I understand no dealer can program a used fob to work on an SKS (silver logo on the back) system.

 

Yes, it is possible to have 4 remotes programmed for one car but getting a USED silver logo remote to be fully functional is almost impossible. As far as I know nobody has ever gotten a used silver logo remote to work.

 

I agree with jelloslug. I purchased 3 2004 to 2008 fobs on ebay, and four different dealers in Pa. and Fl.could not program the silver logo fobs as smart key or remote door unlocking. they were able to program them as starting the car by inserting the fob in the immobilizer slot, ( there are a whole bunch of posts/threads on this site on how you can do your own programing to use fobs as a slot starter. Just search for programming sks fob.) None of them were able to tell me why this could not be
done.

easted

 

I also have a used silver logo fob also and I was able to get it to work in the slot to start the car but that was it. A new fob is only about $130 and programing it should be no more that $50.