Enjoying your ASUS ZenFone 2 yet? You can still make the most of it by installing a CyanogenMod 12.1 ROM instead of using just the basic Android 5.0 Lollipop. Ansebovi, a Senior Member at XDA, was generous enough to share a step-by-step guide for the platform to run on the ZenFone 2.
Ansebovi warns that flashing the CM12.1 in your ZenFone 2 will void the warranty. Only the variant 551ml of the ZenFone 2 is supported for now. Make sure you unlock the bootloader and you have the following files: Asus Zenfone 2 drivers saved on your PC and ADB also installed on your PC. Other items will be mentioned in the detailed instructions so download and install them as instructed.
First, unlock bootloader from this thread and follow all the instructions. Once you’ve unlocked the bootloader, download untethered twrp from this page then turn off phone. Plug the usb cable in your smartphone port, hold the VOL UP buttin, connect other end to the PC port. The green Android robot should appear and when it does, you’d soon see a blue line below the “Waiting Fastboot command or Continue the fastboot process” message.
Choose the folder with the twrp.img by pressing Shift + Right Click> Open command here. Copy and paste the following code–fastboot flash recovery twrp.img– in the command prompt window. Flashing will continue and once done, unplug the phone, and then boot phone. Download CM12.1 from here and the gapps here. Move the download CM.zip and gapps.zip to a microSD card.
Turn power off then hold down VOL UP button, hold the power button until it vibrates. Release power button once vibration stops and wait until the green Android robot appears again. When you see the message prompt “Waiting Fastboot command”, click VOL DOWN until you see Recovery mode then click power button.
Once it enters twrp, take your backup for future use, choose wipe then advanced wipe, select everything except for the micrSD, and then untick internal storage. Click install then choose the externalSD, search for the mentioned zip files, install CM.zip and the Gapps.zip. Reboot phone and then it’s done.