Cannot connect to “au LTE 4G” network (PLMN is 44051) with EC25J module

We are developing a voice communication device using EC-25J(STD).

Currently, we are successfully making voice calls using the following carrier sims

However, with the following carriers’ sims, the connection fails.
KDDI au VOLTE Network (PLMN=44051)

The following command is used to unlock the facility lock.


If the status was “+CLCK: 1” with the above command, release it with the following command

AT+CLCK=“PF”,0, “12341234”
AT+CLCK=“PN”,0, “12341234”
AT+CLCK=“PU”,0, “12341234”
AT+CLCK=“PP”,0, “12341234”
AT+CLCK=“PC”,0, “12341234”

Is there a missing command to unlock the facility lock for KDDI sim?

Hello Tadahiro_Murakoshi, thank you for your question
You can follow the steps below to troubleshoot

  1. Execute AT+CPIN? command to check if the SIM card is locked
  2. Execute AT+QMBNCFG=“LIST” to check whether the MBN file is activated
  3. Execute at+qcfg=“ims” to check the configuration of IMS
    If the MBN file is not activated, you can contact the local FAE and agent through to confirm the reason for the inactivation and obtain the latest MBN file. Thank you.

Thank you for your answer.

When I ran the command you gave me, I got the following.



+QCFG: “ims”,0,0

The result was that the SIM card was not registered with IMS.

What should I do after this?

Hello, Japan KDDI only supports LTE network standard. If you need voice calls, you can only use Volte.
+QCFG: “ims”,0,0 indicates that the module or SIM card does not support IMS service and cannot perform Volte. Quectel EC25-J supports Volte function. Please confirm whether your KDDI SIM card supports Volte, thank you.