After replacing the entire display assembly on my iPhone 6 Plus, everything seemed to be okay, except for one thing. The Touch ID sensor was not working for some reason, and it wouldn't respond to my fingerprint touches. The home button itself was working, and I could press it to go back to the home screen or call up the multitasking view.
When I went to the Settings app, Touch ID option was disabled. When I tried to re-enable it, the process immediately failed, showing the above on the screen. Also, the Reachability function that brings the screen area down half way did not work, either. This relied on lightly touching the home button quickly twice, so it must have been recognizing the fingerprint to function.
The bottom connector on the Touch ID cable wasn't in good condition
I remembered that the Touch ID cable on the display assembly's shield plate got weak while applying heat to loosen the adhesive. Thinking that maybe the connector was damaged, I ordered some replacement shield plates with the Touch ID cable on them.
Replacement shield plate with data cable for the display assembly
Barring a couple of key components, you can order pretty much any 3rd party replacement parts from China, even for iPhone 6 Plus. The shield plates arrived in the mail in a nicely wrapped package.
Heat dissipation sticker for the shield plate is ready
Now the problem was that the plate was missing a heat dissipation sticker, so it was different from the original. So I found a supplier that sold the stickers and ordered some.
Completed replacement shield plate & cable on the left, and the original on the right
I put the sticker onto the shield plate, and now the replacement part was practically the same as the original. Now I was ready to have it installed on the display assembly.
Replacement shield plate installed on the display assembly
With the new shield plate & Touch ID cable on the display assembly, I went onto reassembling the phone, hoping that this would fix the Touch ID troubles.
And I was relieved to find out that the replacement fixed the problem nicely. The Touch ID option was automatically re-enabled upon booting, and my old fingerprint data was back as well. Now I could say that everything was back to normal.
Heat dissipation sticker is easily ripped apart
P.S. The heat dissipation sticker is really hard to peel off without getting ripped. If you were thinking of just buying the cable to fix this sort of issue, I would advise against it.