The FPLMN list (aka forbidden network list) is stored on a SIM and tells a device which networks it can't connect to. It reduces connection attempts to unavailable networks, but sometimes needs to be cleared during debugging.
Why is there a FPLMN list on the SIM?
FPLMN lists are helpful because they tell a device which networks it shouldn't attempt to connect to. This reduces connection time as unavailable networks are ignored when the device is searching for networks.
How does it work?
It's a dynamic list that is maintained by the device. When a device attempts to connect to a network and is denied, it will write that network to the FPLMN list, thus preventing it from attempting to connect to that network 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.
If the SIM has since been activated or networks added to the network-whitelist and you are still not seeing a connection, you will need to clear the FPLMN list. This is because the device will not attempt to connect to networks in the FPLMN list while the sim is in automatic network selection mode. You can also read more on how devices use PLMN lists on the SIM during automatic selection.
How do I clear the FPLMN (forbidden network) list?
Note: This requires knowledge of how to use AT commands on your device and you may need to speak to the manufacturer. Otherwise, try the different approaches below.
You'll need access to the device with the SIM in it and be able to run an AT command. You can first check that it needs clearing by running the standardised AT command:
If you get any response other than 24 Fs (the list's data prefix), then the FPLMN needs to be cleared. To do clear the FPLMN list, you just need to run this AT command:
This will set the list back to the prefix only, meaning that the FPLMN list is clear.
Warning: Some devices/cellular modules require them to be in a specific mode before clearing the list. Please consult your hardware manual beforehand for any specific settings needed - and please remember to change it back to normal operation afterwards!
What if I don't have access to AT commands?
Another If you dont have access to AT commands, there are a couple ways you can use the GSMA standards to attempt to clear the FPLMN list. It requires the device to be within reach (physically or options available on the device - for example manual selection could be set using bluetooth).
Make sure that the network-whitelist has been updated to include the required of the networks for the device to connect to. If the SIM was activated at the time, you will see network-logs of networks the device tried to connect.
Manual Network Selection
Way to clear a network from the FPLMN list is to use manual selection mode. Most devices allow manual network connection in their configuration settings.
during manual selection, your device will not look at the FPLMN list and if successful data connection is made, the device will clear the network from the SIM's FPLMN list.
Taking the SIM out of the device
Some devices will clear the FPLMN list when a new SIM is inserted into it. If you are using plastic SIMs and the device is within reach, take it out and turn the device on. Then turn it off again and put the SIM in again. When it turns on, if it tries to connect to a network that was originally on the FPLMN list, it would mean that device cleared the SIM.
Using a Mobile
Take the SIM out of the device and put it in a phone. If the phone does not clear the FPLMN list, use manual selection as described above to clear individual networks on the list. If the phone does not connect to any network in manual selection, FPLMN list is not the problem and it is something at a network operator level.
This is a bit more drastic, but if the device changes countries and the new country is on the whitelist it will be able to connect again. There are 4 slots in the FPLMN list. As the device changes location the FPLMN list will slowly be updated removing previous entries, clearing the list.
Do you have an Onomondo SIM card? If no, you will need to contact the company that supplies you your SIM card to find out why the SIM is still not working. It could be other issues not related to the forbidden list, such as lack of commerical agreements in the country you are trying to roam in.
If you are still unsure about how to clear the FPLMN list on an Onomondo SIM or have any questions, please write to our support team.