The Cyanogen OS 12 OTA (over the air) update for OnePlus One has started a few days ago with ‘OK OnePlus’ voice activation feature. It will update the OnePlus One to Android 5.0.2 Lollipop and bring new features and revamped Material Design UI to the device. However, some users want to go back to the previous Cyanogen OS 11 (Android 4.4 KitKat) for certain reasons.

If you want to go back to the stock Cyanogen OS 11S firmware, read on to know how it is. You might want to reinstall official firmware on OnePlus One for various reasons. For instance, after rooting and trying out few custom ROMs, if you want to g to the stock ROM, or if it stuck at boot loop after flashing a wrong ROM or whatever reasons your OnePlus One needs stock firmware.

How to Downgrade OnePlus One to CM 11S from CM 12S

Warning: This method will wipe your device completely, so backup your data first.

  1. Download stock Cyanogen OS 11S zip file [HERE] and unzip the file (Use 7zip)

  2. Download 16GB OPO.zip [HERE] or 64GB OPO.zip [HERE] depending on your phone. Unzip the file and copy all the content to the firmware folder.

  3. Now, boot your phone into fastboot mode. To do so, switch off your phone, press Volume UP + Power button together for few seconds, then connects your phone to PC via a USB cable.

  4. Download 15-second ADB installer [HERE] and setup it. Copy all the content from firmware folder to the ADB folder.

  5. From the ADB folder, run the script (16gb Model/64gb Model) by double clicking it.

  6. A command window will open and start the flashing process (Do not disconnect your phone from PC). Once the process is completed, the command window will close automatically.

  7. Disconnect your phone from PC and reboot it. Note: The script will unlock OnePlus One’s bootloader before installing the fimware. Follow the on screen instructions. If the phone reboots after unlocking the bootloader then just disconnect the phone, then boot into fastboot mode and the script should continue the installation process. You have now reinstalled stock firmware on your OnePlus One. If you have any query, leave it in the comment section below. (Source – OnePlus)