Touch ID is an essential feature of iPhone and if it starts failing then life can be miserable for you. Mostly iPhone 5s and iPhone 6 users face touch id failure problems as both models have very sensitive sensors and it can work perfectly with little adjustments.
Here are the possible solutions for Touch ID Failure:
Reset Touch ID
Delete your current finger print and add a new one as a little change in your skin due to weather or any other reason will create trouble in your Touch id.
Many problems are resolved with resetting your iPhone and that can work with Touch ID as well.
iPhone 5s and iPhone 6 sensors will stop working if hands are not dried properly. If you are using touch id with wet hands then you must clean your home button and hands.
Multiple Finger prints
You can use multiple finger prints to avoid any trouble or you can add multiple finger prints for the same finger so it can be scanned in every possible way.