AT command reference and troubleshooting cellular modules

Overview

AT commands help you diagnose connectivity, SIM, registration, signal, and SMS issues. This reference includes standard 3GPP commands and vendor variations with example outputs and actions.

Note: Responses vary by vendor and firmware. Use vendor AT manuals in parallel.

1. AT - Basic connectivity check

AT

Response	Meaning	Next steps
OK	Modem responsive	—
ERROR	Not responding to basic cmd	Check serial, baud, power
No response	Host not connected	Verify hardware

2. Identify device: ATI / +CGMI / +CGMM / +CGMR / +CGSN / +GSN

ATI
AT+CGMI
AT+CGMM
AT+CGMR
AT+CGSN
AT+GSN

ATI
Quectel
BG96
Revision: BG96MAR02A07M1G
OK

3. +CPIN? - SIM status

AT+CPIN?

Response	Meaning	Next steps
+CPIN: READY	SIM detected and unlocked	—
+CPIN: SIM PIN	PIN required	Enter with AT+CPIN=“xxxx”
+CPIN: SIM PUK	SIM blocked	Contact SIM provider
+CPIN: NOT INSERTED	SIM not detected	Check tray/orientation
+CPIN: SIM FAILURE	SIM unreadable	Try another SIM
+CPIN: PH-SIM PIN	SIM network lock	Unlock with carrier code

4. +CCID - ICCID retrieval

AT+CCID

+CCID: 891234XXXXXXXXXXXXXX
OK

5. +CREG? / +CGREG? / +CEREG? - Registration status

AT+CREG?
AT+CGREG?
AT+CEREG?

Stat	Meaning	Common causes	Next steps
0	Not registered	Modem off, antenna issue	AT+CFUN=1, check +CPIN?
1	Registered (home)	Normal	—
2	Searching	Scanning	Wait / relocate
3	Registration denied	SIM blocked or wrong RAT	Check SIM/APN
4	Unknown	Transient	Retry
5	Registered (roaming)	Normal for global SIMs	—
8	Emergency only	Weak coverage	Move

6. +COPS - Operator selection

AT+COPS?
AT+COPS=?
AT+COPS=mode,format,oper,AcT

Modes: 0 Auto, 1 Manual, 2 Deregister, 4 Manual/auto fallback
Formats: 0 Long name, 1 Short name, 2 Numeric MCCMNC
AcT: 0 GSM, 2 UTRAN, 7 LTE, 8 LTE-M, 9 NB-IoT

+COPS: 0,0,"T-Mobile",8
+COPS: 1,2,"310260",7

7. +CSQ - Signal strength

AT+CSQ

RSSI	dBm	Meaning	Action
0	≤ -113	No signal	Check antenna
1-9	-111 to -93	Very weak	Relocate
10-14	-91 to -81	Weak	Expect drops
15-19	-79 to -69	Fair	May drop
20-24	-67 to -57	Good	—
25-30	-55 to -45	Strong	—
31	≥ -51	Excellent	—
99	Unknown	Not camped	Check registration

8. +CESQ - Extended signal quality

AT+CESQ

RSRP (dBm) = -140 + rsrp
RSRQ (dB) = -19.5 + (rsrq × 0.5)

9. +CGATT / +CGACT - Attach and activate PDP

AT+CGATT?
AT+CGATT=1
AT+CGACT?
AT+CGACT=1,1

Response	Meaning	Next steps
+CGATT: 1	Attached	—
+CGATT: 0	Not attached	Check SIM, signal, registration

10. +CGDCONT - Define PDP context

AT+CGDCONT=<cid>,"<PDP_type>","<APN>"

AT+CGDCONT=1,"IP","hologram"

11. +CNMI - New SMS indication

AT+CNMI=<mode>,<mt>,<bm>,<ds>,<bfr>

AT+CNMI=2,1,0,1,1

12. +CMGF - SMS message format

AT+CMGF=<mode>

Mode	Meaning
0	PDU (raw hex)
1	Text (human-readable)

13. +CSCA - SMSC address

AT+CSCA?
AT+CSCA="<SMSC_number>",<type>

+CSCA: "+1234567890",145

14. +CMGS - Send SMS

AT+CMGF=1
AT+CMGS="+1234567890"
>Hello World<CTRL+Z>
+CMGS: 45
OK

15. +CME ERROR - Equipment errors

+CME ERROR: 10   // SIM not inserted
+CME ERROR: 30   // No network service

16. +CMS ERROR - SMS errors

+CMS ERROR: 1   // Unassigned number
+CMS ERROR: 27  // Invalid SMSC

17. +CFUN - Functionality level

AT+CFUN?
AT+CFUN=<fun>[,<rst>]

18. +CGEREP - Packet domain event reporting

AT+CGEREP=<mode>,<bfr>

19. +CGPADDR - Show PDP address

AT+CGPADDR[=<cid>]

20. +CGCONTRDP - Read PDP context parameters

AT+CGCONTRDP=<cid>

21. +COPS=? - Network scan

+COPS: (1,"T-Mobile","TMO","310260",8),
       (1,"AT&T","ATT","310410",7)

22. +CSCON - RRC connection status

AT+CSCON?

23. +CEDRXS / +CPSMS - Power saving modes

AT+CEDRXS=<mode>,<AcT_type>,<eDRX_value>
AT+CPSMS=<mode>[,<Requested_PeriodicTAU>,<Requested_Active_Time>]

24. 3GPP reject cause codes

Code	Meaning	Action
2	IMSI unknown	SIM not active
3	Illegal MS	Contact provider
7	GPRS not allowed	SIM plan issue
15	No suitable cells	Move/check bands
33	Service option unsupported	APN issue
40	No EPS bearer	LTE network problem

Appendix - Vendor-specific commands

Quectel

AT+QNWINFO - Network & RAT info
AT+QENG=“servingcell” - Serving cell
AT+QCSQ - Extended signal
AT+QCFG - RAT/band selection

SIMCom

AT+CSERVINFO - Service info
AT+CNETSCAN - Scan with metrics
AT+CSQEXT - Extended CSQ

u-blox

AT+URAT - RAT selection
AT+UBANDMASK - Band mask
AT+UCGED - Cell info

​Overview

​1. AT - Basic connectivity check

​2. Identify device: ATI / +CGMI / +CGMM / +CGMR / +CGSN / +GSN

​3. +CPIN? - SIM status

​4. +CCID - ICCID retrieval

​5. +CREG? / +CGREG? / +CEREG? - Registration status

​6. +COPS - Operator selection

​7. +CSQ - Signal strength

​8. +CESQ - Extended signal quality

​9. +CGATT / +CGACT - Attach and activate PDP

​10. +CGDCONT - Define PDP context

​11. +CNMI - New SMS indication

​12. +CMGF - SMS message format

​13. +CSCA - SMSC address

​14. +CMGS - Send SMS

​15. +CME ERROR - Equipment errors

​16. +CMS ERROR - SMS errors

​17. +CFUN - Functionality level

​18. +CGEREP - Packet domain event reporting

​19. +CGPADDR - Show PDP address

​20. +CGCONTRDP - Read PDP context parameters

​21. +COPS=? - Network scan

​22. +CSCON - RRC connection status

​23. +CEDRXS / +CPSMS - Power saving modes

​24. 3GPP reject cause codes

​Appendix - Vendor-specific commands

​Quectel

​SIMCom

​u-blox

Overview

1. AT - Basic connectivity check

2. Identify device: ATI / +CGMI / +CGMM / +CGMR / +CGSN / +GSN

3. +CPIN? - SIM status

4. +CCID - ICCID retrieval

5. +CREG? / +CGREG? / +CEREG? - Registration status

6. +COPS - Operator selection

7. +CSQ - Signal strength

8. +CESQ - Extended signal quality

9. +CGATT / +CGACT - Attach and activate PDP

10. +CGDCONT - Define PDP context

11. +CNMI - New SMS indication

12. +CMGF - SMS message format

13. +CSCA - SMSC address

14. +CMGS - Send SMS

15. +CME ERROR - Equipment errors

16. +CMS ERROR - SMS errors

17. +CFUN - Functionality level

18. +CGEREP - Packet domain event reporting

19. +CGPADDR - Show PDP address

20. +CGCONTRDP - Read PDP context parameters

21. +COPS=? - Network scan

22. +CSCON - RRC connection status

23. +CEDRXS / +CPSMS - Power saving modes

24. 3GPP reject cause codes

Appendix - Vendor-specific commands

Quectel

SIMCom

u-blox