HL7588 - "Unspecified GPRS Error"


We are using an HL7588 with a roaming SIM supplied in the UK and deployed in the USA.

It is able to connect to AT+T / T-Mobile & works reliably when the system is first switched on.

However, when these units are switched off, shipped & installed in other locations around the USA, about 50% fail with:
“Unspecified GPRS Error”

When the units are returned to the original location they generally appear to work again OK.

Can anyway shed any light on this or the line of questioning we should take with the roaming SIM provider?

We really need to get this fixed so any help would be much appreciated!



Hi David,

Here are some questions regarding the HL7588, SIM, and AT commands:

  1. What firmware are you running? ATI9
  2. What carrier/MVNO are you using?
  3. What are the following showing when you get the “unspecified GPRS error?”
    • AT+COPS?
    • AT+CGREG?
    • AT+KSRAT?
    • AT+KBND?
    • AT+CGATT?



Hi Jon,

Thanks for such a quick response and apologies for a tardy one from me!

+CGDCONT= 3, “IP”, “wlapn4.com”, “”,

+CREG = +CGREG = 0,2

+COPS: 0

+KBND: 00002000

+CGATT: 1 (althought this appeared to toggle between 1 and 0 quite regularly)

Any ideas, anecdotal or otherwise appreciated!



Hi Dave,

+KBND is showing Band 4 (Verizon band) is selected but +CGREG shows that the module is not registered but is searching. The Class 3 APN/CID is usually reserved for Verizon and as such you should only use this if using a Verizon carrier SIM. Please set +CGDCONT=1 with that APN. Let me know then if +CGATT=1 is steady and not toggling. Regards, Jon

1 Like

Hi Jon,

Excuse my ignorance (Im not on s/w side) - but I didnt realise Context IDs had any meaning ?

Thought they were just a reference to a set of parameters for each APN? ie “wlapn4.com+user+pass”?
Or have I misunderstood your point?

PS - thanks for your help!!

Hi Jon - can you have a look at my last response reference Context IDs please?

PS - superb help so far - thx!



Hi David,

I am just back from vacation and so just catching up today. The “Access Point Name” is necessary to establish the data call or session. Try setting the +CGDCONT= 1, “IP”, “wlapn4.com"
Yes, the Context ID’s do make a difference on some networks (i.e. Verizon and Sprint here in the U.S. use Context ID=3). Let me know if you have made any progress…



Hi Jon,

No progress thus far - could really do with a more detailed investigation.

2 different types of roaming SIM are now exhibiting the same behaviour with an HL7588.
SIMs on their home network perform OK.

We are getting CGREG:2,2 & CGREG:2,4 with automatic network selection.
Bizarrely, there is a very infrequent registration leading to a short APN session then a disconnect leading to a zero byte session. Last one was on network 310410 (AT+T).

Please advise what else we might try to diagnose this behaviour with HL7588 and SIMs not on their own network and without any of the Preferred Network Lists populated.

Many thanks


We are switching some of our product from using the HL8548 to the HL7588 and we hope to use the same driver but we get errors with the HL7588 for reasons not covered in the manual. In particular the setting of the APN with:
+CME ERROR: Unspecified GPRS error
comes back with an error every time on the HL7588 but never on the HL8548. The only reason we are using this command is because a bunch of HL8548 modems in our devices deployed in the field last year lost their APN all around the same time… So we put this in the startup sequence for the driver to protect against a repeat “event”.

This leaves me with some ugly solutions:

  1. don’t use the command and hope the APN never gets forgotten
  2. query the cell modem every startup and select the appropriate commands
  3. query the cell modem type once and preserve that flag and select different init codes appropriately
  4. detect APN errors and set APN then
  5. use the command and ignore the errors on the HL7588

Another command that always gets an error only on the HL7588 is:
+CME ERROR: unknown

I ran the selection of queries mentioned above on the HL7588:
+CGDCONT: 1,“IP”,“m2m-east.telus.iot”,“”,0,0,0,0,0,0
+COPS: 0,0,“TELUS”,7
+CGREG: 0,1
+KBND: 00002000