Chosen Solution
So I just replaced the original screen which was cracked on my iPhone 6 against a new one which is not an original Apple screen, I used the old home button which belongs to this phone, but I still get the Touch ID not working error. I did the screen replacement myself. Shouldn’t the Touch ID work as long as you use the original home button that came with the iPhone 6, meaning the home button and motherboard that belongs together, at least on such an old phone as an iPhone 6? I thought that only if you use a totally new home button that doesn´t “match” the motherboard then the Touch ID will not work? Every time I start up the iPhone 6 I get an error message saying that the Touch ID is not working or something along those lines, and when I go into settings and try to turn on the Touch ID function I get an error message. The iPhone 6 has iOS 10.1.1 if that makes any difference, and I would not like to try to update to the latest 11.4.1 or restore the phone unless I know for sure that that will fix the Touch ID. Is there any way to fix this myself (without going to Apple and put a lot of money on such an old phone), or is it totally impossible and I should just forget about the Touch ID function?
You are correct that using the original Home Button is all you need to do to retain TouchID functionality. However, the Home Button and/or the Home Button Link Flex is easily damaged when its being transferred and this is the most likely issue you are facing. Open up the phone again and closely inspect the Home Button itself. It has a tiny flex that goes to the connector but also a tiny flex that loops back on itself on the other side as well. Use magnification and check for tears. If the problem is with the Home Button itself, then there is nothing you can do, only Apple can replace it. The other possibility is the Home Button Link Flex. This flex runs underneath the heat shield and has a connector at either end to “connect” the Home Button to the logic board. What typically happens is that the flex is damaged when removing the HB, usually because people use a sharp tool to disconnect the connectors. Again, use magnification to inspect this carefully. This flex can be easily replaced by following this guide.
You can try to open the phone up again and try to reconnect all the connectors. If that doesn’t work then you may have to try to restore. You can restore without upgrading if you restore on the phone itself.
