Android Marshmallow for Asus ZenFones
How to unbrick Asus Zenfone 2 and resolve bootloop issues ASUS

Asus Zenfone 2 users can now easily unbrick and recover their device from bootloop issues, following a soft-brick or a hard-brick resulting from changes made to system files or accidentally deleting some system apps while rooting or performing similar hack operations.

If your Zenfone 2 is bricked and stops rebooting or gets stuck at boot logo or leads to force close errors, then you can fix these issues by simply reinstalling the base firmware back on the device.

The best part of this unbrick method is that it offers a pre-rooted firmware with root access for Xposed, titanium backup and several such root-based apps.

If you don't want root access on the phone, you can simply launch SuperSU on the pre-rooted firmware and hit Unroot option under settings. Now, your device will get unrooted and re-enable you to install OTA updates.

IBTimes UK reminds readers that it will not be held liable for any damage to device, during or after the unbrick process. Users are advised to proceed at their own risk.


  • The instructions provided in this tutorial are meant for Asus Zenfone 2 with model numbers ZE550ML and ZE551ML. Verify the model number of the device by going to Settings > About Device
  • Download the necessary firmware file depending upon the base firmware (Z008 or Z00A) installed on the device:
  • Back up important files on the device before you proceed, so that you can restore your important data if something goes wrong while unbricking the device.

Steps to unbrick Asus Zenfone 2 and resolve bootloop issues

  1. Download the pre-rooted firmware files from the download links above. While the firmware is being downloaded, perform steps 2 and 3.
  2. Install ADB drivers.
  3. Install Asus Zenfone 2 drivers.
  4. Enable USB debugging on your Zenfone 2 as follows:
    • Go to Settings > About phone, and then tap 'Build number' seven times to unlock developer options.
    • Return to Settings and select 'Developer options'. Locate 'USB debugging' option and hit the toggle button to enable it. Accept the warning message by tapping OK button.
  5. Connect your phone to PC now and a pop-up message should appear on your phone, when you connect for the first time after enabling USB debugging. Enable 'Always allow from this computer' checkbox and then hit OK button.
  6. Create a new folder on the desktop of your PC, and name it as 'z2unbrick'.
  7. Move or copy all the downloaded files to the z2unbrick folder.
  8. Extract the system.img file from zip files like .zip, .z01, .z02, etc. by using unzip software like winzip or 1-zip. To do so, right click on the .zip file and select extract here option or right click on .z01 file, and select any extract here option. You should get system.img file.
  9. Verify that you have the following files in z2unbrick folder:
  • system.img
  • boot.img
  • droidboot.img
  • recovery.img

10. Now, open command window in the z2unbrick folder as follows:

  • Left click on empty white space in the z2unbrick folder.
  • Now, hold Shift key and right click on empty white space to get a pop-up message.
  • Now choose Open command window here option from the context menu.

You will see a command window open up, with location directed to the z2unbrick folder.

11. Boot your Zenfone 2 into fastboot/bootloader mode by typing the following command into the command window: adb reboot bootloader.

You will see Fastboot written in the middle of the screen. Alternately, you can reboot into fastboot mode as follows: Power off your device, and then hold Power and Volume up buttons together until you see Android logo with fastboot written on the screen.

12. Test if fastboot is working correctly by typing the following into the command window and then hitting enter key: fastboot devices

At this moment, you should get a serial no. with fastboot written after it. If you don't see fastboot written on cmd window, then it means you need to reinstall adb and fastboot drivers, or restart PC, or try connecting via original USB cable.

13. Install the pre-rooted firmware now.

14. Flash the firmware with the following commands by running them one-by-one. Hit enter key after each command.

fastboot flash fastboot droidboot.img

fastboot flash recovery recovery.img

fastboot flash boot boot.img

fastboot flash system system.img

The last command may be time consuming, as the system.img is a huge file.

15. Perform a factory reset, so that you don't face any force close or sluggish performance when using the device. Run the following commands one-by-one to accomplish this task:

fastboot format userdata

fastboot format cache

16. Now, reboot your device with the following command.

fastboot reboot

17. Your Zenfone 2 should start fine now and you should not face any force close errors either. You can unroot the device if you want to install OTA updates in the future. To unroot, launch SuperSU app, go to Settings > select and tap on 'Full unroot' option and then hit 'continue' to remove root access from device and make it OTA compatible instantly.

[Source: The Android Soul]