The FPLMN list or forbidden network list is stored on a SIM and tells a device, which networks not to connect to. It reduces connection attempts to unavailable networks but sometimes needs to be cleared during debugging.
Why is the FPLMN activated on the SIM?
As it tells a device which networks not to connect to, which reduces connection time as unavailable networks are ignored from consideration when the device is searching for a network to attach to.
How does it work?
It is a dynamic list, which is maintained by the device. When a device attempts to connect to a network and it is denied, it will write that network to the FPLMN list, preventing it attempting to connect to it again.
How can it cause problems?
If a device is turned on when a SIM is not activated or if a device goes into a country that is not on the network-whitelist attached to the SIM, the device will write all local networks it tries to connect to onto the FPLMN list and until cleared the device will not attempt to connect to those local networks again.
How do I clear the FPLMN (forbidden network) list?
Note: This requires knowledge on how to use AT commands on your device and you may need to speak to a manufacturer.
You will need access to the device with the SIM in it and run an AT command. You can first check that it needs clearing by running the standardised AT command
If you get any response more other than the first 24 F'S (the list's data prefix) then the FPLMN needs to be cleared. To do this, you run the AT command:
This will set the list back to the prefix only, meaning that the FPLMN list is clear.
If you are still unsure or have any questions, please write to our support team.