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.)
Also download LG Flash Tool and unzip, you should find two files, a Setup EXE file and a DLL file.
Run the Setup EXE file by double-clicking on it and install LG Flashtool.
Once done installing LG Flashtool program, uncheck “Run LGFlashTool” and click on “Finish”.
Step 4. Next, copy and paste MegaLock.dll file to C:\LG\LGFlashTool directory.
Step 5. Open up Device Manager on your Windows computer. (Go to Control Panel->Hardware and Sound->Device Manager)
You should see under Ports (COM & LPT), “LGE Mobile USB Serial Port”. If you don’t see it, you don’t have LG Drivers installed.
Download and install LG Drivers and come back to Step 5.
Double-click on “LGE Mobile USB Serial Port” if you don’t see COM41.
Step 6. Go to Port Settings->Advanced.
Then set your COM Port Number to COM41 and click on “OK”. LG Flashtool software will not work unless you do this that is why we are doing this.
Step 7. Open up LG Flashtool software, you should see a window like below:
This is where we will set the DLL file and stock firmware.
Check “Select Manual Mode” ON, then set the DLL to the DLL file you downloaded earlier. And also set S/W to the stock firmware .tot file you unzipped earlier. And hit “OK”.
Step 8. Click on the Right Arrow button at top left of LG Flashtool software.
Step 9. After checking your files, it will say “READY!!”. When you see that, unplug your G3 micro-USB cable, wait about 3 seconds, then plug it back in.
Step 10. After a minute or two, LG Flashtool will begin installing the factory stock firmware.
Step 11. When it’s done flashing, you should see “PASS!!” and also number 3 on your LG G3 screen. Congratulations! You’ve successfully flashed LG G3 stock factory firmware!
Step 12. Pull the battery out, then in, and your phone should boot. You should see the welcome screen just like the first day you got the phone.
Your LG G3 is now completely unrooted/unbricked with 100% stock factory firmware. Your internals storage should also have been wiped off completely.
Credits – XDA <— Huge thanks to the XDA community as I would not have been able to make this tutorial without y’all!