Calls that drop the moment the customer raises the phone to their ear are the classic proximity-sensor symptom. On the iPhone 12 Pro family it is one of the easiest recurring repairs you can add to your ticket mix — parts cost is low, repair time is short, and a phone that otherwise "works fine" feels broken to the owner without it.
Why the sensor fails after screen swaps
The iPhone 12 Pro moves the proximity sensor off the main display flex and onto a separate short flex cable that sits between the front camera bracket and the logic board. When a tech replaces the screen without transferring (or replacing) this short flex, the sensor loses its data path. The phone still rings, still shows video, but the screen does not turn off during a call — which looks like the screen is broken.
What you need for the job
- iPhone 12 Pro proximity sensor flex (compatible with 12 Pro and 12, identical geometry)
- Y000 screwdriver, plastic spudger, anti-static tweezers
- Display adhesive cut for the 12 Pro frame
- Lint-free cloth and isopropyl for cleaning the sensor window
Step-by-step
- Power the phone off and open it using standard pentalobe + tri-point procedure.
- Disconnect the battery first, then lift the display connector bracket.
- Remove the earpiece speaker / sensor bracket — three screws, fragile plastic tabs.
- Unclip the sensor flex from the frame. Note the orientation pin before you lift — it has only one correct position.
- Compare the new flex against the old one. Transcribe the serial label if your supplier does not pre-print it.
- Seat the new flex, refit the bracket to 0.8 N·m, reconnect the battery last.
- Boot into Settings > Phone and place a test call to verify the screen turns off at the ear.
Tips that save rework
If the sensor still does not fire after a new flex is fitted, the sensor window itself is dusty. Wipe with isopropyl, do not touch it with a gloved finger — oils act as a permanent blocker for the IR beam. Spare sensor flex cables and full iPhone 12 display assemblies are stocked together at ScrnFix so you can bundle the order.
FAQ
Does this affect Face ID? No — Face ID has its own dot-projector flex. The proximity sensor is independent.
Can I reuse the original flex if it isn't torn? Yes, when the part was not the cause. Most shops replace it anyway because the bracket install cost is the same.