Main status check — look for state: and signal quality:
mmcli -m 0
Confirm modem is visible to the system
ls /dev/ttyUSB*
If no devices appear, the problem is at the kernel/USB level — skip to reboot
Possible States
state:
Meaning
registered
Healthy — modem is connected to the carrier network
searching
Trying to find / re-lock onto the network — often a signal issue
disabled
Modem is present but not active — try --enable
failed
Something is wrong — recovery or reboot likely needed
Recovery — try in order before rebooting
1
Enable the modem
sudo mmcli -m 0 --enable
Good first try when state is disabled or failed
2
Reset the modem
sudo mmcli -m 0 --reset
If --enable didn't help
3
Last resort
full system reboot
Required if ls /dev/ttyUSB* shows no devices at all
Notes
If ls /dev/ttyUSB* shows no devices, the problem is at the kernel/USB level — --enable and --reset won't help because ModemManager can't see the modem. Reboot is your only option.
If ttyUSB* devices are present but mmcli shows a bad state, --enable or --reset have a good chance of recovering things without a full reboot.
Low signal quality can cause the modem to drop into searching or failed, but failures are also caused by driver issues, power management, or ModemManager losing track of the modem — not always a signal problem.
A reboot is effective because it reinitializes the modem hardware, restarts ModemManager, reloads kernel drivers, resets the USB subsystem, and clears any stuck processes — a complete clean slate.