Chosen Solution
I was recently given a Mac Air 2018 which was dead with moisture damage. I managed to get it going but ran into security issues. The previous owner and I went to the Genius Bar - so no ID issues, and they reverted it to factory settings and reinstalled Big Sur, but the fingerprint key does not work. Can anything be done?
If the damage was to the Audio board area, then you would need to retain the original Power button/Touch ID board to be able to get finger print to work. If you’re still using that button, then it’s possible the circuitry inside the Touch ID module was damaged by the liquid. I believe on these models (T2 models), the Touch ID module CAN be replaced by Apple, independent of the logic board, (just not vice versa and on older models they need to be replaced together regardless). But in order for Touch ID to function, Apple needs to perform the Touch ID replacement so it can be paired with the logic board as part of the repair.
Sadly, the TouchID and logic board are married there is no means to swap out a damaged TouchID without also swapping out the logic board.
If there is water damage without destroying the sensor chip and the security chip, it is very possible to repair. Just clean the board, find and replace whatever components shorted and corroded.
