Causes of Touch ID not working

[MacUse-R]

I know there are threads about this, but I wanted to start my own thread since the threads I have been reading have a bit different circumstances.

So my iPhone 6 has had its Touch ID working fine until it all of a sudden stopped working. The phone had a broken screen and I have done a screen replacement myself a long time ago and the Touch ID has been working fine after the screen replacement, i used the original home button when I replaced the screen.

Now the new screen is broken again, so i have the phone opened up, and also had to restore to the latest iOS 12.2 through iTunes, and Touch ID was still working after that. So Touch ID has been working fine even though the screen is broken and even after restoring /updating to 12.2.

But then all of a sudden after a phone restart the Touch ID stopped working.

The only thing I can think of is that since the phone is opened up and the screen is laying loosely on top of the phone and only attached by the screens 4 flex cables to the logic board, that the long home button flex cable that runs beneath the heat shield has come loose (on the logic board side) while the phone was on, or that the same cable was reseated while the phone was on? And also i don't have the metal piece installed which goes over and pushes down on the screen connectors on the logic board.

I have tried restoring through iTunes again and have also inspected the connectors on the logic board and the screen with a microscope, connectors looks good, I also tried restoring from an old backup.
None of these things have helped.

So any ideas what might trigger the Touch ID to get disabled.
It feels this Touch ID function is a hit and miss, sometimes it works after screen replacements but sometimes it gets disabled for totally no reason, i have had the Touch ID get disabled on other iPhones after screen replacements even though doing every thing right and being very careful, and obviously using the original home button.

So its hard to get a grasp on exactly which different things causes Touch ID to get disabled, since in all my cases it has happened without no reason, at least without any of those documented reasons which might disable Touch ID.
Also I have a feeling that if Touch ID has gotten disabled it will always stay disabled even if the faulty condition that triggered Touch ID getting disabled are removed, or am I wrong on this? Since I have never gotten Touch ID working again once it has gotten disabled.

Any ideas what might have caused this to happen in my case?

 

[Lekro]

Touch ID is a special breed.

Your case is probably a loose connection either at the TID flex directly or at the motherboard end. If not, it’s either the cable under the heat shield or the TID flex itself then it’s GG.

iPads and iPad minis with TID break if you leave the battery connected when removing the TID, while iPhones don’t.

Same goes for Face ID. While repairing, you have to act like nothing happened as far as Apple’s biometric authenticators concerned.

 

[MacUse-R]

Touch ID is a special breed.

Your case is probably a loose connection either at the TID flex directly or at the motherboard end. If not, it’s either the cable under the heat shield or the TID flex itself then it’s GG.

iPads and iPad minis with TID break if you leave the battery connected when removing the TID, while iPhones don’t.

Same goes for Face ID. While repairing, you have to act like nothing happened as far as Apple’s biometric authenticators concerned.

Thanks for the reply. Actually now all of a sudden its working again. I did remove the battery connector and then removed the 4 flex cables from the logic board, and then i installed them again, and now the Touch ID works.
So it seems you are correct, it was most likely a loose connection, even though i always make sure I get the "click" noise/feel when i attach the flex cables.

While i was at it i opened up my iPhone 6+ which also had its Touch ID disabled after a screen replacement, in the case of the 6+ i suspected that the Touch ID flex cable was broken at the Home button side, since it was very hard to remove it even with heat applied and i had to work it pretty good. It left a visible "kink" in the cable just beside the connector.
Anyway, i had a brand new heat shield/flex cable for the 6+ which i hadn't installed since that flex cable also had a sharp bend at the edge of the heat shield (the flex cable had been pressed against the metal edge causing this bend).

So i was not hopeful when i installed the new heat shield/flex cable, but it seemed to work, at least so far. I made sure not to take the plastic off from beneath the connector this time, since the flex cable connector is very hard to remove without breaking it when its glued to the screen assembly.

So 2 Touch ID´s fixed today (knock on wood).