The module detaches or cannot attach to the network, what to check?

First you need to make sure that the antenna is connected.
Then set:

  • AT+CMEE=2 for extended error replies from AT commands in case of error
  • send AT+CPIN? to verify the SIM status

The following commands could be used to get more information:

  • AT+CSQ? - get the signal strength (only a good indicator for 2G)
  • ATI1 to read FW version
  • AT+CGDCONT? to read the configured APNs
  • AT+CREG=2 and AT+CEREG=2, AT+CGEREP=2 to activate network related URCs
  • AT+COPS? and AT^SMONI to check the operator information and network parameters on a regular basis, especially when connectivity problem occurs
  • AT+CEER=0 on start and AT+CEER in case of network issue detected
  • AT+COPS=? can be used to scan the available networks - it takes some time to get the reply

In some special rare cases, when the module cannot attach to the network at all, while it was working before, the following could be also checked:

Reading FPLMN:

Reading the last EF (0x6F7E) LOCI (Location information):

Reading EF (0x6F53) LOCI_GPRS:

Reading PS LOCI:

Clearing FPLMN list:

Clearing EF_LOCI:

Clearing GPRS LOCI:

Clearing PS LOCI:

Reboot the module and check if it can attach.