Why the device cannot register with the operator


I have used SL6087-firmware 7.51 for 1 years and have recently encountered a serious problem. It will be very grateful if anyone can help me.

My application reads data from uart port and sends it to a remote server via GPRS. Everything seems to be fine but after a time running, some devices (about 5% and increasing) lost the connection with the operator. The led does not blink and i cannot call it. However the application was still working because there were still some right messages sent from the uart port.

I logged into flash the state of sim and the result of at+creg. The result respectively is: ADL_SIM_STATE_FULL_INIT and at+creg returns 2 (not registered, ME currently searching for a new operator).

The weird thing is that the device will continue to work if i unplug and plug the power supply.

I don’t know why the device cannot register with the operator even though it is restarted by at+cfun=1 command in the application after 30 minutes polling creg status unsuccessfully

Thanks & Best regards,
Pham Viet Sam


Did u checked the signal strength AT+CSQ

Does it mean that device will register again to the network? and does the issue happens after u unplug and plug the power supplyy?

can u share the application so that i can test at my end…


Dear Rex_alex,
Thanks for your help,

Yes i did. AT+CSQ returned 29,0, which means the signal strength is fine.

I mean the device registers again to the network only after i unplug and plug the power supply. Soft reset with at+cfun=1 by application itself did not help as i said. And after a time running, the problem may potentially happen again.

It is difficult to reproduce the problem because it happens randomly with the rate of 5 percent as i said. I still don’t know what might be the cause :neutral_face:


as the problem is not systematic, it becomes difficult to get the root cause…

you can get l3rr and mmt level of traces to see what exactly is happening…
i believe you can go to your distributor. he will help you in opening a ticket with sierra wireless team to analyse the traces as the issue could be really important.
When u said 5% of the devices… i beleive quite a bunch of devices are there in the field…
Is it happening with different network providers?
different sim card of same network?


We had a similar problem on a WMP modem, we sent the modem back to Sierra Wireless and they confirmed it was a hardware fault inside the actual module. Does your problem happen on specific units only, or across a number of units intermittently?


Dear Rex_alex,
Yes, i will raise an issue to my distributor.

Could you please tell me what l3rr and mmt level of traces is and how to use it?

Yes it happens with any sim card from different network providers.

Dear tomridl,
Thanks for your helpful information.

It happened across number of units intermittently. Is it same to your case?



You can install developer studio.
After installing, in the target mannagement console, you can see the trace configuration symbol. Use that to select and capture the traces.



Dear Rex_alex,
You mean the “Traces view” tab and “Backtraces view” tab? I know those but they are only suitable to development period. My error devices are already deployed on the real system. The problem happened intermittently and randomly, which i cannot reproduce in our lab. Is there any way to capture any clue about the problem?


An idea would be to try AirVantage Management Service. It is possible to do remote trace on Open AT devices like the SL6087. But remote debugging is only available with FW 7.52 so you would have to upgrade first. But this is also possible through AVMS. There is a free trial of AVMS that you can try.



I’ve the same issue on FXT009 with firmware 7.47.4.
You should log +WCER unsolicited result code and check when a device cannot register if one or several +WCER errors occur.

From SiWi advice, if a +WCER error occurs, you should do a power off/on of the modem.



Dear krima919,
Thanks for your suggestion. I will investigate AirVantage Management Service.

Dear MichaG,
Thanks for your helpful information. According to you, the error is related to hardware?
I will log if any +WCER unsolicited event is raised. However, i am wondering whether there is any risk if Critical Error Report unsolicited indication is enabled (AT+WCER=1) like modem hang instead of modem reset?

You mean i should reset modem by AT+CFUN=1 command? I did but that did not work. Note that my modems are deployed on real sites. Could you share some ways of working around?


Hello sambk87

For my case, the problem appears in a city center fully covered by tower cells of the operator. So YES I think it’s a hardware problem.

You can enable this unsolicited response as the others like +WIND, +CREG, +CGREG, … without any problem.

I mean that a simple reset by AT+CFUN=1 is not always sufficient to correct the problem. The only effective solution is a physical power off/on of the modem.
Attention all +WCER messages do not require a reset or power off/on.
A critical +WCER error is 0x1000.
I suggest you to start to log +WCER and give us your log results.



Hello everyone,
I experience similar issue with HiloNcV2 and HL6528RD but I do not find +WCER in the AT commands guide.
Could you tell me the meaning of +WCER command in order to find an equivalent for the my modules?
Thanks in advance