To ensure stability, a minimum requirement of 5V / 2A power supply is required to power the device. Any power supply with current capacity of less than 2A may damage the module and/or hardware.
It is recommended to use an official Raspberry Pi power supply.

• Check the compatibility of SIM with the module from the SIM provider. The compatibility includes the supported region and frequency band information. Also, check the supported bands of the module from the product specification. 
• Check the SIM card slot for any damaged pin. With a damaged pin, your SIM will not be recognized.
• Confirm the micro-SIM(3FF size) SIM card is inserted in the right direction.

• Confirm that the APN(Access Point Name) is correct. If it’s wrong, your device won’t be able to get on the proper cellular network and transfer data. The APN is unique to each vendor and, sometimes, to each different type of SIM card you buy from that vendor such as AT&T SIMs have APNs of m2m.com.attz & nxtgenphone.
• Check the authentication type and credentials(username and password) with the SIM provider if required. It could be PAP or CHAP.

• Make sure the right antenna is connected to the right port/interface.
• Make sure the female u.FL connector of the antenna is connected/snapped firmly to the male u.FL connector of the module.

Ensure that the HAT has the power to operate. In order to check it see if the POWER LED is lit.

From the physical level without any Linux driver, the Linux OS should recognize USB device included Vendor ID (VID), Product ID (PID).

Check all USB devices with lsusb , if the correct vendor ID and product ID are seen, then USB connection is OK. If any of this info is missing there are several possibilities of this missing information. These are:

• The USB is not connected or the USB cable is damaged.
• The module is not powered or inserted in the HAT.

Supported USB driver VID, PID list:

Applicable Modules and USB Interface Information

If the operating system recognizes the modem, devices named /dev/ttyUSBx are created. You can check if the ttyUSB(s) are available under the /dev directory. Expected outputs are as follows:

For Quectel:

For Telit:

If any of the ttyUSB(s) is missing, then check the drivers according to the OEM’s Guides:

• Telit Modules Linux USB Drivers Software User Guide

• Quectel Modules Linux USB Driver User Guide

Both UART and USB can be used to communicate with the module. To check if everything is fine with UART:

• Make sure the module used with the Base HAT is UART compatible from technical details.
• Follow the steps mentioned in the UART Configuration guide.
• Make sure the serial of the Raspberry Pi is enabled and the serial console is disabled. To know the details of UART and the how-to disable linux serial console please visit https://www.raspberrypi.org/documentation/configuration/uart.md

The essential details that you will control with AT commands are listed below.

AT+CGREG? and AT+CREG? AT commands returns the registration status of the device.

Response:
+CREG: <mode>,<stat>
Possible values are:

0,0 Not registered, ME is not currently searching a new operator to register to
0,1 Registered, home network
0,2 Not registered, but ME is currently searching a new operator to register to
0,3 Registration denied
0,4 Unknown
0,5 Registered, Roaming

Confirm that the device can recognize the SIM.

AT+CPIN? should return READY.

AT+CSQ AT command returns the signal strength of the device.

Response:
+CSQ: <rssi>,<ber>
Possible values are:

<rssi> - received signal strength indication
0 - (-113) dBm or less
1 - (-111) dBm
2..30 - (-109)dBm..(-53)dBm / 2 dBm per step
31 - (-51)dBm or greater
99 - not known or not detectable

<ber> - bit error rate (in percent)
0 - less than 0.2%
1 - 0.2% to 0.4%
2 - 0.4% to 0.8%
3 - 0.8% to 1.6%
4 - 1.6% to 3.2%
5 - 3.2% to 6.4%
6 - 6.4% to 12.8%
7 - more than 12.8%
99 - not known or not detectable

Check the PDP context parameters such as PDP type (IP, IPV6, PPP), APN, data compression, header compression etc. your module is trying to use, with the command: AT+CGDCONT?
Possible responses are:

+CGDCONT: 1,"IPV4V6","vzwinternet","",0,0
+CGDCONT: 2,"IP","super","0.0.0.0",0,0

Support Request

Please attempt the solutions recommended in this guide before contacting Support or Community. If these don’t resolve the issues, report your issue in community by answering the form questions below.

Please be as specific as possible. Basically, tell us what steps we need to take to create the issue, what you expected to happen and what actually happened.

• Describe Your Problem:
• Use Case Scenario:
• Environment
• Raspberry Pi Model / SBC:
• Operating System (OS):
• HAT:
• Antenna:
• Mini PCIe Module:
• SIM:
• Other peripherals, if any:
• Cellular Connection Type(PPP - QMI - ECM):
• Service or Script Logs:
• Outputs of the following Linux commands:
• cat /etc/os-release
• uname -a
• lsusb
• lsusb -t
• usb-devices
• dmesg | grep tty
• ls -l /sys/bus/usb-serial/devices
• ls -l /dev/serial/by-id
• Responses to all AT commands listed below:

Quectel Modules	Telit Modules
AT	AT
ATI	ATI
AT+QGMR	AT+CGMR
AT+CPIN?	AT+CPIN?
AT+CPAS	AT+CPAS
AT+CFUN?	AT+CFUN?
AT+COPS?	AT+COPS?
AT+QCFG=”usbnet”	AT#USBCFG?
AT+QCFG="band"	AT#BND?
AT+CREG?	AT+CREG?
AT+CGDCONT?	AT+CGDCONT?
AT+CSQ	AT+CSQ
AT+CGATT?	AT+CGATT?
AT+QCFG="nwscanseq"	AT+GMM
AT+QCFG="nwscanmode"	AT#SWPKGV
AT+QCFG="iotopmode"	AT#FWSWITCH?
AT+QCSQ	AT+CGREG?
AT+QNWINFO	AT#CGPADDR=

AT Commands Manuals List

• Quectel EC25&EG25 AT Commands Manual
• Quectel UC20 AT Commands Manual
• Telit LE910Cx AT Commands Reference Guide
• Telit ME910C1 AT Commands Reference Guide