How To Fix a Quectel EM120R-GL LTE Modem On Ubuntu

PlexyDesk — Thu, 26 Mar 2026 17:34:13 +0000

This guide documents a working fix for a Quectel EM120R-GL PCIe LTE modem on a Debian/Ubuntu style Linux system using NetworkManager and ModemManager.

It was validated on a machine with:

Quectel EM120R-GL
Device ID 1eac:1001
A Sri Lanka SLTMobitel SIM
NetworkManager
ModemManager

The same pattern may also apply to other Quectel MBIM modems that are fcc-locked on Linux.

Symptoms

The modem is physically present, but mobile data does not come up on Linux even though the same SIM and modem work in Windows.

Typical signs:

lspci -nn shows the modem, for example:

05:00.0 Unassigned class [ff00]: Quectel Wireless Solutions Co., Ltd. EM120R-GL LTE Modem [1eac:1001]

mmcli -L shows no modem because ModemManager is not running, or it shows the modem but activation fails.
nmcli device status shows the WWAN device as disconnected or stuck connecting.
The ModemManager journal shows repeated messages like:

couldn't enable interface: 'Invalid transition'

The raw Quectel MBIM vendor state shows:

sudo mbimcli -d /dev/wwan0mbim0 --quectel-query-radio-state

and returns:

Radio state retrieved: 'fcc-locked'

Root Cause

On Debian/Ubuntu-style systems, ModemManager ships FCC unlock scripts for some integrated WWAN devices, but they are not always enabled by default.

For this modem, Linux saw the hardware and the MBIM ports correctly, but the modem radio stayed fcc-locked. That prevented the software radio from turning on, which caused ModemManager to loop with Invalid transition errors.

In this case, the sim-pin2 status reported by ModemManager was not the real blocker. Data started working once the FCC lock was cleared.

Step 1: Make Sure ModemManager Is Installed and Running

Check package and service state:

dpkg -l | rg -i 'modemmanager|network-manager|libmbim|libqmi'
systemctl status ModemManager --no-pager

If ModemManager is installed but inactive, enable it:

sudo systemctl enable --now ModemManager

Verify the modem appears:

mmcli -L

Step 2: Confirm the FCC Lock

Check the modem and raw MBIM radio state:

mmcli -m 0
sudo mbimcli -d /dev/wwan0mbim0 --quectel-query-radio-state
sudo mbimcli -d /dev/wwan0mbim0 --query-radio-state

If the vendor radio state says fcc-locked, continue.

Step 3: Enable the Quectel FCC Unlock Hook

On Debian/Ubuntu systems, the Quectel FCC unlock helper is usually already installed in:

/usr/share/ModemManager/fcc-unlock.available.d/

For the EM120R-GL device ID 1eac:1001, enable it with:

sudo ln -sfn /usr/share/ModemManager/fcc-unlock.available.d/1eac:1001 \
  /etc/ModemManager/fcc-unlock.d/1eac:1001

Then restart ModemManager:

sudo systemctl restart ModemManager

Step 4: Verify the Modem Registers on the Mobile Network

After restart, check:

mmcli -m 0
sudo mbimcli -d /dev/wwan0mbim0 -p --quectel-query-radio-state

You want to see:

modem state: registered
power state: on
operator name: SLTMobitel or your carrier
packet service state: attached
Quectel radio state on

Step 5: Bring Up the Mobile Connection

If NetworkManager already created a profile, activate it:

nmcli connection show
nmcli connection up 'Mobitel 4G'

If needed, re-enable autoconnect:

nmcli connection modify 'Mobitel 4G' connection.autoconnect yes

If you need to create a profile manually:

nmcli connection add type gsm ifname '*' con-name 'Mobitel 4G' apn mobitel
nmcli connection up 'Mobitel 4G'

Step 6: Verify Real Internet Traffic Over WWAN

Check address assignment:

nmcli -f GENERAL.STATE,GENERAL.CONNECTION,IP4.ADDRESS,IP4.GATEWAY,IP4.DNS,IP6.ADDRESS device show wwan0mbim0
ip addr show wwan0

Force a test over the WWAN data interface:

curl -4 --interface wwan0 https://ifconfig.me/ip

If that returns a public IP, mobile data is working.

Notes About Routing

If Wi-Fi is also connected, Linux may keep Wi-Fi as the default IPv4 route while the WWAN link is still healthy and usable.

Check default routes:

ip route show default
ip -6 route show default

If you want the SIM to be the preferred route even while Wi-Fi is up, you can either disconnect Wi-Fi or lower the WWAN route metric in NetworkManager.

Useful Diagnostics

These commands were useful during diagnosis:

lspci -nn
lspci -k -s 05:00.0
ip link show
rfkill list all
nmcli general status
nmcli device status
mmcli -L
mmcli -m 0
mmcli -i 0
journalctl -u ModemManager -u NetworkManager -b --no-pager
sudo mbimcli -d /dev/wwan0mbim0 --query-radio-state
sudo mbimcli -d /dev/wwan0mbim0 --quectel-query-radio-state
sudo mbimcli -d /dev/wwan0mbim0 --query-pin-state

Why It Worked in Windows but Not Linux

Windows often ships vendor integration that clears the regulatory lock automatically for laptop-integrated WWAN modules.

Linux had all the right drivers here:

mhi-pci-generic
mhi_wwan_mbim
mhi_wwan_ctrl

but the FCC unlock hook was not enabled, so the modem stayed radio-locked until the ModemManager helper was explicitly turned on.

Persistent Fix Summary

The persistent fix was:

sudo systemctl enable --now ModemManager
sudo ln -sfn /usr/share/ModemManager/fcc-unlock.available.d/1eac:1001 \
  /etc/ModemManager/fcc-unlock.d/1eac:1001
sudo systemctl restart ModemManager
nmcli connection modify 'Mobitel 4G' connection.autoconnect yes
nmcli connection up 'Mobitel 4G'

After that, the modem registered on LTE and internet traffic over wwan0 worked normally.

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Starting on new file manager for for PlexyDesk

PlexyDesk — Fri, 06 Mar 2026 06:19:10 +0000

GPU-accelerated desktop compositor for Linux - No it's not Wayland or X11

PlexyDesk — Wed, 25 Feb 2026 16:44:11 +0000

PlexyDesk. A display server and desktop shell written in C/C++ that renders everything with OpenGL SDF shaders, real-time Gaussian blur, glass materials with refraction and chromatic aberration. The goal: macOS-level visual polish on Linux, without bolting effects onto an existing compositor.

What it does today

Glass materials : multi-level blur, fresnel rim lighting, and refraction
SDF rendering : resolution-independent rounded rects, per-corner radius, elevation shadows
macOS-style dock : icon magnification, bounce-to-launch, running indicators
Genie minimize | GPU mesh deformation, just like macOS
Window physics | cloth simulation with spring damping - compiz like
Widget toolkit | buttons, sliders, text input, flexbox layout — all GPU-rendered
Zero-copy buffer sharing | clients submit DMA-BUF frames, no copies
X11 app support | Firefox, GTK apps, etc. via integrated Xwayland

PlexyDesk implements its own display protocol optimized for GPU-rendered UI. Clients render locally using libplexycanvas (SDF shaders, FreeType text, flexbox layout) and submit frames over Unix sockets. A client crash doesn't take down the compositor.

It's reaching the point where real apps run on it. Firefox works. GTK apps work. The dock launches apps. Windows minimize with a genie effect. There's still a lot to do but the hard parts (the protocol, buffer sharing, the rendering pipeline) are working.

I'm building this in the open and would love feedback from anyone interested in Linux graphics, compositor internals, or just making Linux desktops look better.

Star the repo, open issues, or just say hi on discord [https://discord.gg/7ckXmcns] I'll be posting build logs here as the project progresses. and to read more about plexydesk visit [https://plexydesk.com]

DEV Community: PlexyDesk