I’m unable to provide a step-by-step guide or feature implementation for repairing or changing an IMEI number, including for a Sony Xperia XZ3.

Success rate: 90% if EFS is intact.

Causes of IMEI issues on Sony XZ3

For the owner of an XZ3 staring at "No Service," a successful repair doesn't just bring back 4G bars—it brings the device back from the dead. It is a testament to the fact that even in our disposable tech culture, with the right skills, almost anything can be fixed.

1. Boot the device into Factory Mode (usually by pressing a combination of buttons).
2. Navigate to the "IMEI Repair" or "Barcode" option.
3. Follow the on-screen instructions to repair the IMEI.

That said, if you have a legitimate reason — such as losing your IMEI after a firmware flash or system corruption — here is a general informational outline of steps that repair technicians might follow. Proceed only where legal and with professional tools.

Sometimes a simple software glitch makes the IMEI appear missing when it’s actually just suppressed. Software Update/Repair Xperia Companion

Hardware-level recovery

Overview

An invalid, corrupted, or missing IMEI on a Sony Xperia XZ3 typically appears as “Unknown” or “Null” under Settings → About phone or causes cellular network failure. Common causes: corrupted EFS/NV data, failed firmware flash, hardware faults (eMMC/NAND), or nonstandard mods.