The FPLMN list (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 shortens the time it takes to connect because the device won't look for networks that aren't available.
How does the FPLMN list work?
It's a dynamic list that is maintained by the device’s cellular module. When a module 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 the FPLMN list 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 safelist, the device will write all local networks it tries to connect to to the FPLMN list.
If the SIM has since been activated and you are still not seeing a connection, you should try clearing 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?
The following options require knowledge of how to use AT commands on your device. You may need to speak to the manufacturer or supplier if you are unfamiliar with AT commands.
Clear the FPLMN list with AT+CRSM
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 standard AT command:
The AT+CRSM command tells the SIM to give us the FPLMN datafile (28539) in binary (176). If you get any response other than 24 Fs (the list's data prefix) as shown above, then the FPLMN needs to be cleared.
To clear the FPLMN list, you can run the update binary (214) AT+CRSM command with 24 F’s:
This will set the list back to the prefix only, meaning that the FPLMN list is clear.
Warning: Some cellular modules need to enter a specific mode before clearing the list. Please consult your hardware manual beforehand for information on specific settings – and please remember to change it back to normal operation afterwards.
Manual network selection with AT+COPS
Another way to remove a network from the FPLMN list is to use manual selection mode. Most modules allow manual network connection in their configuration settings.
Run the manual network selection AT command on the forbidden networks:
During manual selection, the module will not look at the FPLMN list. If a successful data connection is made, the module will clear the network from the SIM's FPLMN list.
Warning: A few cellular modules will not attempt to manually connect to a forbidden network. Please consult the manufacturer’s AT Command Manual for more information
You can read a full overview of the network selection command here: AT+COPS.
What if I don't have access to AT commands?
If you don't have access to AT commands, there are a couple ways you can use the GSMA standards to attempt to clear the FPLMN list.
Take the SIM out of the device
Some devices will clear the FPLMN list when a new SIM is inserted into them. 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 card in again. When it turns on, the device will try to connect to previously forbidden networks if it has successfully cleared the SIM.
Use a phone
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 options on the phone to clear individual networks on the list: go to network selection in the settings menu, choose manually select networks, wait for the phone to scan the networks in the area (this can take a couple of minutes), and then pick a network to connect to.
If the phone does not connect to any network with manual selection, the FPLMN list is not the problem; it is most likely something at the network operator level.
This is a bit more drastic, but if the device changes countries and you have access to more networks, it will be able to connect again. There are four slots on the FPLMN list. As the module meets new networks, the FPLMN list will slowly be updated, removing previous entries and clearing the list.
Do you have an Onomondo SIM card? If not, 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 commercial 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.