How To Set Up A Lg Phone

Assuming your LG G3 is on the latest version of Android available for the device, there likely isn't a root that is compatible with it. So, to achieve the root, and then custom ROM, we'll need to downgrade the device (back to Kitkat in this case) first.

Before you start that however, you'll want to ensure there is an active LineageOS build for your specific LG G3 version, as not all devices might be supported. https://wiki.lineageos.org/devices/

1 - Downgrade:

Download and Install the LG Mobile Drivers. Click "Software & Firmware" on the following page
1. https://www.lg.com/ca_en/support/support-mobile/lg-LGD852
Download and Extract the LG Up Files
1. https://oceanhost.eu/545euinlq0hw/LGUP_LG_G3.zip.htm
Install " LGUP_8974_DLL_Ver_0_5_CODEFIRE.MSI " followed by " LGUP_Install_Ver_1_14_3.msi "
Download and extract the respective KitKat file for your device. Our phone is a D852, and we will be using the Bell version specifically. Ensure you select the appropriate ROM for your device.
1. https://storagecow.eu/index.php?dir=Xda%2FLG+G3%2FStock%2F
2. Canada D852 > BELL D852AT-01-V10b-302-610.zip
On the device, go into Settings > General > About phone – and tap "Build Number" until it says "You are now a developer"
Go back, then into Developer Options, and Enable USB Debugging
1. Note: USB Debugging will be greyed out if the device is plugged in, so make sure it's not.
Plug the phone into a USB 2.0 port, then swipe down to open the notification tray and change your USB mode to MTP Mode.
On the PC, open LGUP as Administrator, select the .tot file, Refurbish mode and then hit start.
1. If it doesn't detect your device on open, try a different USB port, or a different PC.
Congrats, you should now be back on KitKat.

2 - Rooting / Flashing LineageOS:

If you've just downgraded, quickly setup the phone, and reenable USB Debugging. ( Repeat Steps 5 to 7 in part one )
Download the PurpleDrake root
1. https://forum.xda-developers.com/lg-g3/development/root-root-lg-g3-easily-purpledrake-lite-t2821000
2. Check the following compatibility chart to see if you're support, and to see what other root you might use if you're not.
  1. https://docs.google.com/spreadsheets/d/1hs0qlcGP80gl9wC0r9bs0AWMD-1D9iGgC9ulCG9roMs/edit#gid=0
Plug in the phone, if it's not already, and run PurpleDrake as admin.
1. You might have to re-plug the phone, or restart the root program if it doesn't detect the device.
2. Select Yes to allow USB debugging with this Computer when prompted on the device
3. Select Yes to permanently rooting with PurpleDrake.
Download the new version of TWRP and copy it over to your device
1. https://forum.xda-developers.com/lg-g3/development/recovery-teamwin-recovery-project-lg-g3-t3813552
Download the TWRP App onto the device from the Play Store and open it.
Backup your recovery if you wish via the TWRP app, and then copy it over to your PC
Select the TWRP file we copied over earlier in the app, flash it to recovery, and then reboot to recovery
Once in the TWRP recovery, select Backup, and swipe to backup your install of KitKat with TWRP incase anything goes wrong later in the process. Copy that over to your PC from the TWRP folder.
Back in the main TWRP menu, select Wipe>Advanced Wipe, and select Dalvik / ART Cache, Cache, Data, Internal Storage, and System – then swipe to wipe.
Download the latest build of LineageOS, selecting the correct version for your device. Copy it to your device.
1. https://wiki.lineageos.org/devices/#lg
Download the latest Open Google Apps – ARM, Android 8.1, and Nano. Copy it to your device.
1. https://opengapps.org/
Back on the device, select Install in TWRP, select the LineageOS zip and swipe to Install. Then select the OpenGoogleApps zip, and swipe to Install that.
After 5-10 minute it will complete and reboot the phone into LineageOS. Hurrah!
1. Setup the phone and install any missing Google Apps as necessary from the Play Store.
2. *Optional* Download the install the Magisk root in TWRP

Helpful Side Notes:

Here's a great video on how to enter recovery mode w/o using the TWRP app: https://www.youtube.com/watch?v=waFrzMQivaI
- Note: It wont actually factory reset the device if you have a custom recovery installed.

How to Flash an LG G3 Back to Stock (2015 method from this post: https://forum.xda-developers.com/showthread.php?t=2785089

There are a couple different methods, but I found the most consistent was to use LG FlashTool V1.8.1

Download and extract the KitKat .tot file, and the DLL file, for your respective device (assuming you don't already have it)
1. https://storagecow.eu/index.php?dir=Xda%2FLG+G3%2FStock%2F
Download and install LG FlashTool V1.8.1 (don't run it yet)
1. https://oceanhost.eu/nskpvk76ezvp/Setup_LGFlashTool_1.8.1.1023.exe.htm
Download the Megalock DLL file, and copy it to C:\LG\LGFlashtool, replacing the existing Megalock file (this might be a hidden folder, so enable viewing of those)
1. http://oceanhost.eu/o9n2mef5f2no/MegaLock.dll.htm
Power off the phone
Press and hold the Volume Up key and then plug the phone in, it should now be in "Download mode"
Open up Device Manager on your PC, navigate to "Ports (COM & LPT), select the one related to LG or "LGEModem", navigate to the Port Settings tab, click Advanced, and change the COM port to COM41, and then click "Okay".
Run LG FlashTool as Admin, click "Select Manual Mode", select the DLL file for the DLL slot, select the .tot file for the "S/W" slot, and click "OK".
Select the big yellow right arrow in the top left. The COM41 box should change to say "READY!!". It should say something along the lines of "Waiting for connection" below that. If it doesn't, try replugging the device.
Once it's done (it might show as failed in the software), you should be presented with a screen on the phone saying "LG Factory Reset Status" with a big number 3. Pull the battery and the phone should restart as normal.
Now you can update the device back up to Marshmallow with OTA updates, or with the LG Mobile Support Tool.