Unlock, Re-lock Sony Xperia S And U Bootloader

We have to relock Sony Xperia S or U bootloader, when you’re going to submit your phone to the Sony service center (not only them, all the devices need). Because of you have to submit non-modified phone. If you have rooted and unlock bootloader phone, they will refuse the warranty. In-addition to that, sometime after the unlock the bootloader you may not receive updates via OTA. So this tutorial I’m going to show you how to relock your Sony Xperia S and U bootloaders. If you search unlocking read this guide.

  • Fully charge the phone
  • Fully backup the phone ( guide in here)
  • Enable USB debugging (Settings>Developer options)


This is not a risky process, if anything goes wrong, your device can be bricked. Applying this method at your own risk. I can’t claim the damages. This method only for the Xperia S and U devices.


  • Install the downloaded flashtool and run the application.
  • Copy your device downloaded relock bootloader “.ftf” files, into the “C:\Flashtool\firmwares” folder.
  • Power off the phone and wait for a few seconds.
  • Press and hold the “Volume Down” key and same time connect the phone to the computer. If Windows starts install fastboot drivers, wait for a few seconds to complete the installation. Now you can see your phone LED turn to green.
  • If flashtool display “Device connected in flash mod”, you can go to the next step. If it fail to identify your phone install the drivers and follow the process again.
  • Click Flashtool “Thunder” symbol contains icon.
  • In the “Mode selector” window tick “Flashmode”
  • Firmware selection windows, choose the correct relock bootloader firmware
  • Finally click “OK” button, now it starts the installation process.
  • When the relock bootloader ftf file installation complete, flash stock firmware using flashtool.
  • After all the installation complete, disconnect the phone from the computer and power on.
  • Now you can verify your bootloader locked. Go to dial pad and type *#*#7378423#*#*
  • Navigate to “Service>Configuration” if it displays “Bootloader unlock allowed:Yes”. You relock the bootloader.

Now install stock ROM using PC companion, Sony update service.

[via:XDA forum]

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