Shaunyf100

I have a 2010 BMW 535xi and I recently replaced the HPFP with a used one and seems to be working perfectly fine, but ever since I put everything back together I've had this error. From what I've read it could be the alternator, battery or something within the transfer case but the battery is brand new (haven't registered it to the car but has same specs as previous battery) alternator seems to be working properly, so its pointing to the transfer case but I'd like to not have to open up that can of worms if possible, I've also noticed the engine shutters slightly and starts idling a bit lower than normal a few minutes after I start the car. Any tips or other possibilities on why I'm getting this fault code? Thanks in advance.