For those of you who may soft-brick your LG G3 (soft-brick is when you are stuck in a bootloop), want to return your phone back for warranty, or simply want to return back to 100% stock, here’s a step-by-step tutorial you can use.
First, you will need a Windows computer as LG Flashtool program does not support other operating systems. (You may be able to use VMWare on Mac or Linux, it should work.) This should work on all Windows including Windows XP, Windows 7, Window 8, and Windows 8.1. (I am using Windows 7 64-bit, I just don’t like Windows 8 that much.)
By unrooting/unbricking your LG G3, YOU WILL LOSE EVERYTHING on the internal storage of your LG G3! So, PLEASE MAKE A BACKUP of everything you need to backup before preceding! (YOU’VE BEEN WARNED!!!!)
Step 1. How to get into Download Mode?
First power off your LG G3 or you can also pull the battery out then in. Then while holding the Volume Up button down, plug in a micro-USB cable from your computer.
Step 2. You should see your phone showing “Download Mode”.
Then it should turn to “Firmware update” screen.
Step 3. Go to our LG G3 Stock Factory Firmware page and download appropriate firmware and DLL file for your LG G3. (If you don’t see your model, try Googling it first.)
Unzip the stock firmware zip file, you should get a folder with a file that end in .tot. (You may have to enable hidden extensions on Windows to see .tot, if you don’t see the extension, don’t worry about it and go to the next step.)