Overview
This guide explains how to diagnose and troubleshoot common problems encountered when using Siretta industrial cellular modems. It covers serial communication, SIM card issues, network registration, LTE diagnostics, packet data failures, socket communication problems, GNSS troubleshooting, network reject causes and modem recovery procedures.
| Part Number | Description |
|---|---|
| ZETA-GEP-LTE4 (EU) | Low Power LTE Cat 4 European Modem with GPIO and GNSS |
| ZETA-NEP-LTE4 (EU) | Low Power LTE Cat 4 European Modem with GPIO |
| ZETA-N-LTE (EU) | High Performance LTE Cat 4 Modem with GPIO |
| ZETA-NSP-LTE1 (EU) | Low Power LTE Cat 1 Modem |
| ZETA-NLP-LTE1 (EU) | Ultra Low Power LTE Cat 1 Modem |
| ZETA-G-GPRS | GSM/GPRS Modem with GNSS |
| ZETA-N2-GPRS | GSM/GPRS Modem |
This guide demonstrates how to:
Expected Result
At the end of this guide the modem should be capable of being systematically diagnosed and restored to normal operation.
Before troubleshooting software or network issues:
The first diagnostic step is verifying serial communication with the modem.
| COM3 - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
AT |
| Expected Response | Meaning |
|---|---|
OK |
Modem communication operational |
| No response | Serial communication failure |
| Garbled characters | Incorrect baud rate |
Important Note
Most communication failures are caused by incorrect COM port or serial settings.
Verbose modem errors provide significantly improved diagnostics.
| COM3 - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
AT+CMEE=2 |
| Command | Description |
|---|---|
AT+CMEE=2 |
Enables verbose error reporting |
SIM card problems are one of the most common modem issues.
| COM3 - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
AT+CPIN? +CPIN: READY OK |
| Response | Meaning |
|---|---|
READY |
SIM operational |
SIM PIN |
PIN entry required |
SIM NOT INSERTED |
SIM missing |
SIM PUK |
SIM permanently locked |
The modem must successfully register on the network before:
| COM3 - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
AT+CREG? +CREG: 0,1 OK |
| COM3 - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
AT+CGREG? +CGREG: 0,1 OK |
LTE-capable Siretta modems use EPS (Evolved Packet System) registration.
When operating in LTE mode:
AT+CEREG? should be usedAT+CREG? may not provide valid LTE registration information| COM3 - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
AT+WS46=28 |
| COM3 - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
AT+CEREG? +CEREG: 0,1 OK |
Siretta modems support advanced diagnostic commands which provide detailed information about:
These commands are extremely useful when:
| COM3 - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
AT#CEERNET #CEERNET: EMM - PLMN not allowed OK |
| COM3 - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
AT#CEERNETEXT #CEERNETEXT: EMM CAUSE 11 - PLMN NOT ALLOWED OK |
| Cause | Meaning |
|---|---|
| PLMN NOT ALLOWED | Network operator rejected SIM |
| EPS SERVICES NOT ALLOWED | LTE services unavailable |
| ROAMING NOT ALLOWED | SIM roaming restriction |
| GPRS SERVICES NOT ALLOWED | Packet services barred |
| NO SUITABLE CELLS | No compatible LTE cells available |
| ILLEGAL UE | Device IMEI rejected |
| ILLEGAL ME | Device barred by network |
Poor RF conditions are a major cause of modem instability.
| COM3 - Tera Term VT |
¶ File Edit Setup Control Window Help |
|
AT+CSQ +CSQ: 18,99 OK |
| CSQ Value | Signal Quality |
|---|---|
| 0-9 | Poor |
| 10-14 | Fair |
| 15-19 | Good |
| 20-31 | Excellent |
| Command | Purpose |
|---|---|
AT+CMEE=2 |
Verbose modem errors |
AT#CEERNET |
Network reject diagnostics |
AT#CEERNETEXT |
Detailed LTE reject diagnostics |
AT+CREG? |
GSM registration |
AT+CGREG? |
GPRS registration |
AT+CEREG? |
LTE EPS registration |
AT+CSQ |
Basic signal quality |
AT#MONI |
Serving cell information |
AT#RFSTS |
RF status information |
AT#SERVINFO |
Detailed serving cell data |
AT#SGACT? |
PDP context status |
AT#SCFG? |
Socket configuration |
AT#SS |
Socket status |
AT#SI |
Socket information |
AT+CGATT? |
Packet attach status |
| Step | Action |
|---|---|
| 1 | Verify serial communication |
| 2 | Check SIM detection |
| 3 | Verify GSM registration |
| 4 | Verify GPRS registration |
| 5 | Verify LTE EPS registration |
| 6 | Check network reject causes |
| 7 | Verify signal quality |
| 8 | Verify packet data configuration |
| 9 | Test socket communication |
| 10 | Perform modem recovery if required |
Support
For further assistance, please contact the Siretta support team.