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I want a new key for my Mercedes Benz and I've heard that you can get a used smart key for much cheaper than a new one from a licensed Mercedes mechanic.

Can I reuse an already programmed Mercedes smart key fob?

I've heard a Mercedes can be programmed to accept a new key, doesn't that mean a used key will work?

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  • Spent a couple hours scouring info about these keys so I thought I'd share in a more succinct manner – Ben Brocka Jun 4 '12 at 14:31
  • This is very helpful information. Thanks a lot everyone. I am also stuck with smart key issues. – user7595 Nov 23 '14 at 6:39
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Any key that has already been programmed to a Mercdes will never work in any other car.

Once a key has been "flashed" or programmed to one car you can't reprogram the key. Mercedes keys pair "for life", so once you stick a key in the ignition and it works, it's never going to work in another car.

It is true that a Mercedes can accept new keys; when you get a new key you usually get an "additional" key, which pairs with the car and programs very quickly. You can have multiple keys that work with a car, but you'll have to get them ordered from Mercedes; dealers can't make them up and they won't have them on hand. You'll have to place an order with your VIN number for them to send you a compatible, fresh key.

There have been claims that you can reprogram a smart key but this is not true once the key has been paired. If you order online and get a used, preprogrammed Mercedes key, it's not going to work. It might not even work with the car it was originally programmed for!

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  • The one thing I never did turn up was an official Mercedes resource on this, though I've confirmed this with a Mercedes authorized dealer. – Ben Brocka Jun 4 '12 at 14:53
  • For future readers. This answer is actually not correct at all. You CAN unlock used Mercedes keys. The older "big" ir fobs with Motorola mcu inside are the easiest. The next gen (small black) and first gen chrome versions with NEC chips inside can also be reset pretty easy. The newer chrome version with bga chips can be unlocked by calculating the password but rarely is it worth the trouble with the price of aftermarket unused fobs being so cheap these days. These are not claims but facts. I have personally done each type many times. This is not common however and only done by specialists. – narkeleptk Oct 1 '19 at 21:13
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get a hot air soldering iron remove the transponder chip from the main board and solder new blank chip on then it can be programmed but you may need a key programmer to do could cost you about £100 total to do but better than £250

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You can use the old key mother board that is in the old key and transfer it to the new key. No need to reprogram it will work. You just need a new key fob not a new key.

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  • Only if that key is already programmed to that car - at which point you've still only got one key... – Nick C♦ Oct 7 '13 at 9:59

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