Quectel EM05CEF not connecting on Ubuntu 22.04 via ModemManager

IoT Modules LTE-A Module
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1

Hello,

I am using a Quectel EM05CEF modem on Ubuntu 22.04. The modem is detected as /dev/cdc-wdm1 and wwan0, and the SIM card is present and ready. However, it cannot register on the network and no data connection is established.

I have tried:

  • Stopping ModemManager
  • Using qmicli commands
  • Checking signal with AT+CSQ

All attempts fail. Other devices with the same SIM card connect fine.

Question:
Why does the EM05CEF modem not work with ModemManager on Ubuntu 22.04? Are there known compatibility issues or required settings?

Thank you.

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2

Dear Zero,

Thank you for reaching out.

From your screenshot and the behavior, you described, Ubuntu is detecting the EM05CEF correctly as a QMI/WWAN modem (/dev/cdc-wdm1 and wwan0). However, the modem is not registering because it is not camping on any cell (the GUI also shows Signal 0% and Network status/type: Unknown).

This is typically caused by RF/antenna issues, weak/no coverage, or the module being locked/misconfigured to unsupported RAT/bands, not a ModemManager compatibility problem.

To isolate the root cause, please share the outputs below:

AT commands (via the modem AT port):

ATI

AT+CGMR

AT+CFUN?

AT+CPIN?

AT+CSQ

AT+CEREG? and AT+CREG?

AT+COPS?

AT+CEER

QMI checks (after stopping ModemManager to avoid port conflicts):

sudo systemctl stop ModemManager

sudo qmicli -d /dev/cdc-wdm1 --nas-get-serving-system

sudo qmicli -d /dev/cdc-wdm1 --nas-get-signal-strength

As a quick recovery step (in case the module is RAT/band locked), you can also try resetting scan mode to automatic and reboot:

AT+QCFG=“nwscanmode”,0

AT+QCFG=“nwscanseq”,00

AT+CFUN=1,1

Once you share the above results, we can confirm whether the issue is RF/coverage/antenna related or a configuration lock and provide the exact fix.

Looking forward to your response.
Thank you.

Best Regards,
Aghelan