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Face ID stopped working after a screen replacement: what actually broke
The two-minute background
Face ID is a system of parts that are security-paired to the logic board: the dot projector, the infrared camera and the flood illuminator. Apple pairs them at the factory; they cannot be re-paired in a shop by software. That design decision, not clumsiness, is why a routine screen job can end with Face ID is not available.
The usual suspects, in order of frequency
- The front-sensor flex was nicked or torn during opening. The module is glued close to the top edge; a pick that goes a millimetre too deep cuts it.
- The connector was not fully seated after reassembly, or a fleck of debris sits in it. This is the case worth praying for — reseating fixes it.
- Moisture reached the module before or during the repair. The IR camera tolerates less than the rest of the phone.
- The wrong module came back. On a board-swap or mixed-parts phone, the TrueDepth assembly answering the bus is not the one this board was paired to. It will enumerate — and refuse to do Face ID.
Telling them apart without guessing
The phone itself knows which case you are in, and says so in two places a diagnostic can read over USB:
- Presence: does the TrueDepth module answer enumeration at all? A torn flex is silence; a pairing mismatch answers but flags itself.
- Panic and error logs: a failing module leaves entries naming the biometric
subsystem —
Pearlin Apple's internal naming — often with a timeout code that distinguishes "no answer" from "wrong answer".
Quote rule: silence on the bus means flex or module replacement plus the pairing limitation conversation. An answering-but-unpaired module means the part is fine and the history of this phone is the problem. Do not quote the second as the first.
What to tell the customer
The honest script: the sensor package is paired to the board by Apple for anti-tampering reasons; if the module itself is damaged, only Apple or an AASP can restore Face ID with a genuine paired part. What a shop can always do is prove which part failed — and put that proof in writing before any money changes hands.
Read it from the phone instead of guessing
PhoneVitals pulls every number in this article off the device itself over USB — the gauge records, the panic logs, the pairing checks — and prints them in a report your customer can verify by QR code. The first scan on your computer is free.
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