Some expert members over at XDA Developers have come up with a way with which all LG G4 variants can get root access now thanks to a new tool. Up until now, it was only the international variant of the G4, which was up for grabs with a different method.
- You must have the T-Mobile variant to use this guide.
BEFORE WE BEGIN
- Download the LG USB drivers  for your computer and install them before connecting the smartphone.
- Download the ADB and fastboot  drivers on your computer.
- Download the rooting package  you need for T-Mobile handsets.
- Download the Send_Commands tool here .
- Do not try using this guide on the Verizon, International or AT&T variants.
HOW TO ROOT T-Mobile LG G4 ON ANDROID 5.1
- Extract the root package to your computer. You should find the .img file inside.
- Transfer that image file over to the internal SD card. Make sure it’s in the root folder and not inside any other folder.
- Extract the Send_Commands tool to the computer. Notice the Send_Command.exe file and the ports.bat file.
- From the same folder that contains the Send_Command file, open the command prompt window by right-clicking the mouse and holding the Shift key. Now choose to open the command prompt windows from the menu.
- Have the G4 disconnected from the computer and reboot it to Download Mode. Completely power it off, re-connect it to the computer while holding Volume Up.
- Double click the Ports.bat file and check which ID port your G4 is connected to on the computer.
- Type the command “Send_Command.exe \\.\COM3” if you connect to COM 3 and alter the number in the code to what number you are connected to if not number 3.
- Type “id” followed by pressing enter.
- Check you get the command “text ‘uid=(0)root gid=(0)root’”. If you do not get that command, it’s important to go through the command line steps again until you get success.
- Type the last command “dd if=/data/media/0/system.rooted.H81110h.img bs=8192 seek=65536 count=548352 of=/dev/block/mmcblk0” and you’re done.
- Wait for it to root your smartphone and enter the “LEAVE” command to finish. Your handset will reboot and you are ready to flash a custom recovery if you need it.