Root LG K40 LM-X420 / Bootloader Unlock & TWRP

LG K40 can be rooted after unlocking the bootloader and flashing a custom recovery such as TWRP. Using the custom recovery we can install a flashable Magisk or SuperSU zip file to root the device.

I’m trying to root my LG K40 MetroPCS with model number LM-X420MM. There are different variants of K40 based on different carriers. The other K40 variants are T-Mobile lmx420tm, AT&T lmx420as, factory unlocked lmx420qn, US Cellular lmx420qm & Spectrum Mobile lmx420qn.

Let’s start the procedure by unlocking the bootloader.

LG K40 Bootloader Unlocking – LMX420MM

To unlock the LG K40 bootloader we need to do the following steps –

1. Turn on the “Developer Options”

“Developer Options” is hidden by default but can be enabled quite easily. Follow this post to enable it on your K40 – LG K40 Developer Options.

2. Enable USB Debugging

After doing the first step, Go to Developer Options and enable USB Debugging.

lg k30 root

3. Connect K40 to PC via USB Data Cable

Now we are ready to connect our phone to the PC via USB data cable.

lg k30 lge mobile adb interface driver

Wait for the LGE Mobile ADB interface driver to install, after connecting the phone.

4. Use Minimal ADB & Fastboot Tool for Bootloader Unlocking

Using Minimal ADB and Fastboot tool, we are going to write the ADB command to boot our K40 into Fastboot Mode.

Launch Minimal ADB & Fastboot tool. You’ll be prompted to enable USB Debugging on your K40 screen.

Tap “OK” to allow USB Debugging as shown above.

Let’s check if our K40 is connected properly and the ADB drivers are installed.

Type adb devices and hit enter on your PC keyboard.

You can see, my device with model number LMX420 visible under the “List of devices attached”.

LM-X420 is the model number of LG K40.


Now Let’s try to boot out K40 into fastboot mode for Bootloader unlocking.

Type adb reboot bootloader and hit enter

It’s our bad luck. The phone reboots into normal mode after writing the adb reboot bootloader command. You can check the above video. I tried it several times with no luck.

lg k30 fastboot mode

The fastboot mode was available in K30 but it’s not accessible in LG K40. The above screenshot belongs to LG K30 Fastboot Mode.

Unless and until we unlock the LG K40 bootloader, it’s not possible to flash a TWRP custom recovery. Thus, K40 cannot be rooted as of now. In the future, if there comes a root method for LG K40, I would update it right away.


Please share your valuable thoughts via the comment section below. Feedback is welcome.




8 thoughts on “Root LG K40 LM-X420 / Bootloader Unlock & TWRP

  1. Im probably way off base from what i gathered fastboot is still there but something about zeroing out the laf partition and crossflashing it with a European variant using the “Frankenstein” method…its kind of complicated and from the looks of it easy to brick your phone if you don’t know what steps to do it in.

  2. That’s too bad. This phone has been out for awhile but as of now there’s still no successful way of rooting the device. Hopefully somebody will come out with something soon.

    • That’s true. Earlier LG Metro / T-Mobile Phones with Android Nougat were all rootable. The newer phones with Oreo and Pie firmware including K30, K40, Aristo 3(Plus), Aristo 4 Plus, Stylo 4 & Stylo 5 cannot be rooted as there is no provision to unlock the bootloader.

  3. Plz someone come out for a root solution to the lg k40 x420MM10n from metro tmobile android v9 i refuse to update because im sure eventually there will be a way hopefully lol?=)

  4. That’s too sad! Thanks for your explanation, other way I would be looking for some method in the internet wasting time. I’ll be watching if you figure out how to do it. Thanks for your job!
    Good luck!

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