Sim card not detected on RM520N-GL


I am currently working with a RM520N-GL modem on our own hardware, and having some problem with it not detecting the sim card. I have tested the RM520N-GL modem in a RM500-EV board with the same sim card and here is works fine.

On our hardware I have also tested with a RM500Q-GL modem, and this modem detects the sim card without any programs. The only thing I had to change was that is had to use sim slot 2, instead of slot 1. This change has also been done for the RM520.

The sim detect pin is pulled down all the time via a resistor and the setting for the detect pin is set to: ‘+QSIMDET: 1,0’

When i do a AT+CPIN is response with: SimNotInserted: SIM not inserted

To communicate with the modem we are running openwrt 22.03 with ModemManager.

Does anyone have an idea of what could wrong or where to look for the error?

You can tyr AT+QUIMSLOT=2 command to switch to SIM slot 2