I went though the same. I reflowed the solder on both my keys. They worked again for a while. Then they stopped.

The weirdest part was: key world work if I slammed the trunk but that even stopped working.

I eventually "bit the bullet" and ordered a real key from online dealer.

Fixed the problem 100%.

It was exclusively the key the entire time! I suspect the same in your case. The original keys have enough bad solder joints they aren't able to sync with the car anymore and the cheap copy just isn't up to snuff.

I was ecstatic when I finally just did it. Worth every penny to have a real key. There is an online actual legit BMW dealer that will save $60 or so. I bought a valet key with the savings.

Search xo for the thread on the subject. It has links to the exact part webpage.

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