When the LTE Modem is not stable, the crashlog will show repeated 'interface is brought up' as follows:
diagnose debug crashlog read
475: 2025-07-17 17:01:28 Interface wwan is brought up. process_id=219, process_name="lted"
476: 2025-07-17 17:17:42 Interface wwan is brought up. process_id=219, process_name="lted"
477: 2025-07-17 17:34:24 Interface wwan is brought up. process_id=219, process_name="lted"
478: 2025-07-17 17:50:58 Interface wwan is brought up. process_id=219, process_name="lted"
The 'lted' debug logs will show 'timeout' errors as follows:
diagnose debug application lted -1
diagnose debug enable
2025-07-17 16:17:11 qmi_dev_read_msg(341)-219: Can not read QMI device 0 : timeout
2025-07-17 16:17:11 usb_qmi_wwan_wds_get_packet_service_status(2956)-219: Failed read msg(No such device)
2025-07-17 16:17:11 sierra_qmi_wwan_check_modem_data_connection(918)-219: wds_get_packet_service_status failed! Tried 1 times!
2025-07-17 16:17:17 qmi_dev_read_msg(381)-219: This message is an indication message, ignore it and read again.
2025-07-17 16:17:27 qmi_dev_read_msg(341)-219: Can not read QMI device 0 : timeout
2025-07-17 16:17:27 usb_qmi_wwan_wds_get_packet_service_status(2956)-219: Failed read msg(No such device)
2025-07-17 16:17:27 sierra_qmi_wwan_check_modem_data_connection(918)-219: wds_get_packet_service_status failed! Tried 2 times!
2025-07-17 16:17:37 qmi_dev_read_msg(341)-219: Can not read QMI device 0 : timeout
2025-07-17 16:17:37 usb_qmi_wwan_wds_get_packet_service_status(2956)-219: Failed read msg(No such device)
2025-07-17 16:17:37 sierra_qmi_wwan_check_modem_data_connection(918)-219: wds_get_packet_service_status failed! Tried 3 times!
2025-07-17 16:17:37 update_modem_status(544)-219: Modem activated success but connection check fails! 544
To stop the debugging, use the commands given below:
diagnose debug application lted 0
diagnose debug disable
diagnose debug reset
Solution.
 The command will allow users to change the modem USB speed ( swap between High-Speed USB 2.0 and Super-Speed USB 3.0).
Important note:
The solution has been verified on the FortiGate-40F-3G4G model. Do not apply these settings to the FortiGateRugged-60F-3G4G model, as it will cause SIM card detection issues. | 
