John,
Yes, for our model year, if you get the FCC numbers on the back of the FOB (from eBay, for instance) to match up, the new one will work...HOWEVER, unlike earlier 850's we can't program these ourselves. I tried and tried. You have to take it to the dealer and have them do it. If you have a good relationship with your dealer they might do it for free. They charged me $25 to do mine. BTW, although your current FOB is broken, if you want to continue to use it (like for emergencies), you'll need to take it in at the same time as the new one when you get it programmed. These have to be programmed in series (1 after another...and up to 3 FOB's). If you don't do this, then the "new" programming for the FOB you buy will delete the programming you already have for the old one. Hope this information helps. Just tell your dealer that you want to have them program a new FOB as the old one you have has had the ring break off on it and is not unsuitable for your needs anymore. Whatever you do, don't tell them you bought the new one from some place like eBay...they're bound to charge you an arm an a leg...just tell them you found it (like in the depths of your glove box or something, but it doesn't work even after replacing the battery in it), or don't tell them anything at all. Good luck!
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.