Fix OTA update failed errors on a Nexus 7 (Requires root)

So you tried to flash Android 4.2.2 and wanted to see it boot into the new version, but instead got an “update failed” message?

There are several reasons why an update could have failed. Two of the most popular reasons you get an update failed error maybe because:

1. You may have downloaded the wrong version or the file may have been corrupted.
2. You might have deleted a system app or made changes to the system files

The update zip includes a script which checks for missing/altered system apps,files. If it finds some file is missing, the update will fail. For example if you deleted Plusone.apk, which is the Google+ app and try to flash the update, it will fail and give you an error relating to plusone.apk

If you think the first reason mentioned above, was the cause, just redownload the proper version and flash it again using a custom recovery. It’s that simple.

But if you think the update failed because you deleted or altered some system app, its going to take a few minutes to get things the way we want. But hey, it can be fixed quite easily.

Disclaimer: We are in no way responsible for any damage that may occur during flashing or any steps mentioned here. Just follow the post at your own risk.

So what you’ll need to do is, download the stock image of 4.2.1 and flash it on your Nexus 7. In other words, we are restoring the tablet’s system stuff to the state it was before you altered it.

Let’s see how to do that.

1. First download the Nexus 7 Toolkit from XDA. Use this link.
2. Install the toolkit on your computer, and run it to install the drivers. (Follow our post here if you need help on how to install the drivers)
3. Plug in your Nexus 7 to it using the USB cable.
4. Choose option 9 to Download and install the stock ROM and flash the stock recovery. Just type in 9 and press enter in the toolkit window to do so. Note: This will erase any custom recovery you may have installed.
5. Type in 1, to download the Stock ROM Image, i.e 4.2.1
6. Once it has downloaded,  choose option 2 to flash the image.
7. When it prompts you to choose if you would like to erase userdata, type in NO.  this should preserve all your installed apps, games, data,etc.
8. Let it finish the flashing process and reboot into the OS.

Congratulations, your Nexus 7 is back in factory state, but with your apps and stuff in it. All you have to do now is just check for an update and install it. Follow our post here to get the latest OS for your Nexus 7.

So keep in mind, never delete a system app, or you will have to go through a similar process the next time an update is available.

Note: You will need to root your Nexus 7 again after you reflash the Stock ROM.