Asus Zenfone 2 (Z00AD, ZE551ML)

I have downloaded the stock firmware from here. But how to flash it? This guide tells me to put it on an external SD card and boot into "update mode" by pressing Power + Volume Down, but that combination doesn't do anything on my phone.

It looks like I can use something called Asus Flashtool, but it appearantly involves using a different type of format for the firmware, which I will need to download from a third party.

Asus has provided me with the firmware. How to flash it?

  • To do this, you have to get into the bootloader using the Power + Vol down key combination as you mentioned. Are you holding these keys starting with a completely OFF phone? If the phone is on when you hold these keys, it will not do anything. If this still doesn't work for some reason, there is another way using the abd tool from the Android SDK. But that is the hard way (unless you already have the SDK installed and know how to use it), so let's try to get the key combo to work first. Jun 23, 2016 at 19:23
  • 1
    @PaulRatazzi Postive, that key combo does nothing (of course, the phone is off.) Power+ Vol UP does do something, though. I think I've found something, this tutorial looks very promising. I'm following it now.
    – Fiksdal
    Jun 23, 2016 at 19:29
  • @PaulRatazzi Success! I'll post an answer with all the details.
    – Fiksdal
    Jun 23, 2016 at 20:21
  • 1
    Glad you got it!! Jun 23, 2016 at 20:22
  • @PaulRatazzi Answer ready.
    – Fiksdal
    Jun 23, 2016 at 21:29

2 Answers 2


I found out how to do it with the official firmware from asus.com. I'll post this for the benefit of all sentient beings future readers with the same problem. I'm writing this in a very beginner-friendly fashion.

Note: I had stock recovery. These steps will not work if you have a custom recovery.

Disclaimer: This is only what worked for me. It may or may not work for others. Follow these steps at your own risk. Any problems you encounter or global nuclear wars you cause while following these steps are your own responsibility. If something goes wrong (such as a power outage or loose cable) in the middle of the flashing, it will soft-brick your phone. If you don't know how to deal with such things, take your phone to a proper service center instead of following this tutorial.
1. I downloaded the official firmware from here.

Important(!): You must select the exact correct file. Failing to do so could damage your device. It's important that you match all the numbers with those on your device. In my case, the relevant values were ZE551ML and for WW. ("WW" is the important part.) You may think you have the same phone as me, but your values may be different. In that case it's very important that you get another image, namely the correct one for your device!!

  1. I used Windows 10.
  2. Downloaded and installed this driver.
  3. Downloaded and installed Minimal ADB and Fastboot.
  4. Copied the firmware file (from step #1) to the folder in which Minimal ADB and Fastboot was installed. (In my case C:\Program Files (x86)\Minimal ADB and Fastboot.)

Before proceeding, ensure the battery is above 50% (just to be safe.)

  1. Turned off the phone completely.

  2. Pressed and held the Power button and the Volume up button both at the same time.

  3. As soon as the phone vibrated, I let go of the power button.

Please note: I had to try several times before this key combination worked. If it doesn't work immediately, try again until it works.

  1. After a short while I saw this:

  1. I pressed Volume down twice until it said RECOVERY MODE inside the box. I then pressed the Power button.

  2. When you see this dead android, and a message saying Error!, do not despair, I also saw that message.

  1. On that screen, I pressed the Power button and the Volume up button both at the same time.

Please note: I had to try several times before this key combination worked. If it doesn't work immediately, try again until it works.

  1. I was then taken to this screen:

  1. I pressed Volume Down to select apply update from ADB. I then pressed the Power Button to select that option.

  2. I connected the phone to the computer.

  3. I navigated to the folder in which Minimal ADB and Fastboot was installed. (In my case C:\Program Files (x86)\Minimal ADB and Fastboot.)

  4. Holding down Shift I right clicked in the white space in that folder and selected Open command window here.

  5. In that window, I typed adb devices and pressed Enter to check the connection to the phone.

In my case, the output to that was

List of devices attached
0123456789ABCDEF        sideload
  1. I then typed adb sideload UL-Z00A-WW- and pressed Enter.

Important: Unless you have the exact same file as me, you have to replace UL-Z00A-WW- with whatever file name your actual firmware file has. Remember to include .zip as Windows often doesn't display file name extensions by default.

  1. The process took around 20 minutes. This time may vary. The command prompt window told me the percents of progress along thew way. I was given a confirmation message after it was done. I rebooted the phone, and I now have the stock firmware on my phone.

I actually also wiped data and cache partition (which wipes all personal data), because I wanted a totally clean phone. But I think that's optional.

Attribution: I followed this tutorial, but I had to do some of the things differently and figure parts of it out on my own.

By the way, I've successfully rooted now, and it works again! :D

  • Nice answer! It should also be possible to apply an update from storage which would eliminate the 2nd computer dependency. Do you not have that option in your system recovery? Either way, all's well that ends well! Congrats! Jun 23, 2016 at 22:15
  • @PaulRatazzi Thanks! Yeah, update from storage is clearly superior. I searched for hours for a way to do it. As I said, Voume down + Power button didn't do anything on my phone. Even when i called Asus support US yesterday, they didn't know how to do it. The only way they knew was to issue adb commands from a desktop computer. But even the support guy had no clue. He was reading from a tutorial and Googling stuff himself. And the tutorial he was following was for a totally different firmware and didn't work at all. I eventually figured it out by reading that tutorial I mentioned earlier.
    – Fiksdal
    Jun 24, 2016 at 5:55

I made a tutorial myself, with some details people might get confused with. Let me know if this helped.

How to install the firmware upgrade on ASUS Zenfone 2.

Pre-requisites: - Firmware desired. - Minimal ADB and fastboot tool. - A computer to install the ADB files and download the firmware. - Phone battery charged. If possible, over 50%.

Go to ASUS official website, download the firmware: IMPORTANT: Make sure the OTA Image SKU (the one you are downloading) is the same as the current Device Image (the version you have installed on the device at the moment). This is very important!: In my case is WW- So the upgrade must be "WW" as well or it will fail. Trust me, it fails at around 20 percent, where the package is validated by the OS. Make sure what your device version is. It can be: WW, CUCC, CN or JP.

Then download the Minimal ADB and fastboot tool. - This is a set of files that will be installed on your hard drive, in the Program Files folder. ADVICE: paste the firmware ZIP file on the same folder as the ADB tool, easier to find.

Turn on the phone on Recovery Mode: - Volume up + Power button. - With the volume up or down search for Recovery Mode. - Power button to accept. The phone will restart on Recovery Mode. - On the error screen press Power button and a quick press of the volume up button, this will skip the so common error this device has. - Scroll down to the option: apply update from ADB. - Now plug the phone via usb and then select this option.

On the ADB console: - If you plugged the phone like the previous step: type "adb devices" (without quotes, on the console. The device should appear.). I would say this is not necessary but you must make sure the phone was recognized, or it won't work. - It should say:

|List of devices attached. 0123456789ABCDEF sideload|

  • Now type "adb sideload filename.zip". Replace filename.zip with the zip file of the firmware. Example: adb sideload UL-Z00A-WW-
  • Enter... and wait for the process to complete, it takes about 25 minutes.

The last thing you should see on your device is Install from ADB complete. Then reboot the system now. The screen should pop up with an Updating Android message, wait until is finished.

Best of lucks.


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