EM061K-GL disappears from USB bus after warm reboot (Linux) - Requires cold boot

IoT Modules LTE Standard Module
1

Hi,

I am experiencing a critical power cycle issue with the EM061K-GL module. After a warm reboot in Linux, the modem completely disappears from the USB bus and cannot be detected until a full cold boot (G3 power loss) is performed.

Here are my system details and the troubleshooting steps already taken:

Environment:

  • Modem: Quectel EM061K-GL (M.2 form factor)

  • Host Device: Sintrones VBOX-3131 (Intel Atom-based Industrial In-Vehicle PC)

  • OS: Ubuntu 24.04.4 LTS (Kernel 6.8.0-107-generic)

  • Interface: Recognized as a USB device (lsusb)

  • Previous Modem: Quectel EM05-G (Worked perfectly on this exact same setup)

Issue Description:

  1. Upon a cold boot (powering on the host PC from zero), the EM061K-GL boots up normally, is detected via lsusb, and works perfectly with ModemManager.

  2. If I perform a warm reboot (sudo reboot in Ubuntu), the host PC restarts, but the EM061K-GL completely disappears from lsusb.

  3. The same issue happens if I force a Suspend-to-RAM (rtcwake -m mem -s 15). Upon waking up, the modem is gone.

  4. The modem remains in this “zombie/unresponsive” state. It cannot be revived via PCI bus reset scripts or USB sysfs unbind/bind commands.

  5. The only way to recover the modem is to completely unplug the power from the Host PC (Cold Boot) or physically remove and reinsert the M.2 module.

Hardware Root Cause Identified: We diagnosed that the Sintrones VBOX motherboard does not drop the 3.3V power to the M.2 slot during a soft reboot or S3 suspend. It keeps the slot energized but resets the data lines. The BIOS is locked for industrial use, meaning there are no “ErP Ready”, “Deep Sleep”, or USB Power control options available to force a VCC drop during reboot.

While the older EM05-G handled this continuous power state during a reboot without any issues, the EM061K-GL seems to crash or enter a protection state when the host resets the bus but maintains VCC.

My questions:

  1. Is there any specific AT+QCFG command to modify the power management or fast-boot behavior of the EM061K-GL so it can survive a warm reboot where the host does not drop VCC?

  2. Since modifying the Host BIOS is not an option, is it recommended to mask a specific M.2 pin to prevent the modem from hanging during the host’s soft reset?

Thank you in advance for your support.

2

Hi there,

Answering to your questions:

  1. Currently, we do not have any command to survive a warm reboot where the host does not drop VCC. Sorry for the inconvenience.
  2. Regarding the M.2 hardware interface, we do not recommend masking or modifying any M.2 pins unless it has been specifically validated by Quectel. Such modifications may introduce unexpected behavior or affect compliance with the module hardware design requirements.

May I confirm whether the host platform can control the M.2 module reset signal (PERST#, RESET#, or W_DISABLE#) during reboot and suspend/resume? If available, toggling the reset signal may help reinitialize the module without requiring a full power cycle.

Thank you