I've repaired a couple of these keys always been broken solder joints. Also the switches fail. The problem with re sync is that you won't be able to reliability bend the board inside to make contact to press the button when needed.

There is a guy that will repair such a problem for about $60 vs replace for $200.

It's rarely the battery but after 15-19 years it's becoming more likely to be battery, but the switches are probably still more likely than the battery.

If you have only one key, get a new one from the dealer, then it will be safe to open up the defective one and fix it. I have some high end solder tools so I can easily reflow all the solder joints. They are small so don't try if it's your first time with small soldering.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)