LG K40 MetroPCS Firmware Download & Update -LMX420MM Stock ROM

The need to flash a stock firmware arises when either you’ve bricked your phone or unable to do OTA (Over the air) System update.

In some cases, the phone bricks when the firmware update process gets stuck in the midway. If your LG K40 is stuck on the firmware update screen then you’re at the right place.

To flash stock firmware /ROM on LG K40 we need to download a few files –

1. LG Mobile USB Driver v4.4.2 setup file – Download and install this file on your PC


2. LGUP Dual Mode.zip  – Download & Extract this file on your computer


3. LG K40 MetroPCS Stock Firmware ROM X420MM10g.zip – Download and extract this file on your computer


LG K40 Stock Firmware / ROM Download & Software Update – MetroPCS LM-X420MM

Let’s divide the whole process into 4 steps for the ease of understanding –

STEP 1: Installing the USB Driver and booting the phone into Download Mode


LG K40 MetroPCS firmware download


I’ve downloaded the above files on my computer.

The first step is to install the LG Mobile Driver.

Double-click the “LGMobileDriver_WHQL_Ver_4.4.2” setup file to start the installation process.


LG K40 Firmware Update Driver

Finish the driver installation following the on-screen prompts.

LG K40 Download Mode Firmware Update

Now, we are ready to connect our LG K40 to the computer in Download Mode.

To boot the phone into Download Mode –

  • Power off the phone
  • Connect one end of a USB Data Cable to the phone and press the Volume Up key as shown above.
  • Keep the Volume key pressed and connect the other end of the USB cable to the computer.

LG K40 Download Mode

Your K40 must be now in the Download Mode. The above screenshot shows the download mode.

LG K40 Firmware Update Driver

Wait for the driver installation to complete.

“LGE AndroidNet USB Serial Port” & “LGE AndroidNet USB Modem” drivers should install successfully as visible in the Device Manager screenshot above.

STEP 2: Installing and running LGUP Flashing Tool

LG K40 LGUP Dual Mode

After the driver installation is successful, open the extracted LGUP_DualMode folder to view the files.

LGUP Store for LG K40

We’ve to install “LGUP_Store_Frame_ver_1_14_3”  setup file.

Double-click the file to start the installation process.

LGUP for Store LMX420MM

Finish the installation and proceed further.


Right-Click the “SetUser” file and select “Run as administrator”.

Approve the request to run the file. A command prompt window will open and close on its own.


Now click the “LGUPU” file to load the LGUP program for flashing.


LG K40 LGUP Loading Env

LGUP is loading

STEP 3: Loading the LG K40 kdz firmware file and Flashing

LG K40 LGUP Bin File

The connected phone is detected as LM-X420MM which is the model number of LG K40 MetroPCS.

The current firmware version is X420MM10d.

We are going to update the Firmware to X420mm10g.

Tap “BIN File” to highlight it.

LG K40 LMX420MM kdz download

Hit the “3 dots” icon to browse for the downloaded kdz file for flashing.

X420mm10g Firmware LG K40

Browse for the downloaded LG K40 Firmware file which is “X420MM10g_00_MPCS_US_OP_0808.kdz” & load it in LGUP.

LG K40 Software Update LGUP

The kdz file is added for flashing.

LGUP FLashing LG K40

Now change the “Process” from “REFURBISH” to “UPGRADE” and tap “START” to begin the flashing.

LG K40 flash in progress LGUP

The Progress bar shows 52%. Do not disconnect the phone until the process is 100% complete.

LG K40 LGUP Flashing complete

At around 80%, the phone reboots.

LG K40 Software Update LGUP

Now the Progress bar says, 100% COMPLETE!


We’ve successfully updated our LG K40 firmware using LGUP.


For queries and suggestions, please use the below comment box.








Leave a Comment