I am having trouble uploading code to my Arduino Nano. It has been very trusty in the past, but I am getting this new error when uploading any code to it: avrdude: ser_open(): can't set com-state for "\\.\COM15"

This happened a while ago on my Windows 11 Laptop, and I was unable to resolve it, and now it has just started on my Windows 10 desktop.

I tried disabling and re-enabling the CH340 in device manager, restarted my computer, and uninstalled the CH340. After uninstalling it, it has dissapeared and does not even show up in Device Manager at all.

If anybody could provide some help explaining how to make it show up in Device Manager again, and also make it uploadable, I would greatly appreciate it!

Thank you in advance

  • 1
    did you try to change the Processor option in Tools menu?
    – Juraj
    Commented Jul 8, 2023 at 15:58
  • @Juraj Yes, I did. I beleive it may have something to do with recent Windows updates, but im not sure.
    – Sky-Wired
    Commented Jul 8, 2023 at 16:20
  • some other program may have possession of COM15
    – jsotola
    Commented Jul 8, 2023 at 17:19
  • @jsotola I dont think so. It switches ports every now and then, and none of them work. i can upload to any other type Arduino. Doesn't matter the port.
    – Sky-Wired
    Commented Jul 8, 2023 at 17:29
  • then the Nano has failed in some way ... check for foreign objects inside the USB connector and on the surface of the board ... also try a different cable
    – jsotola
    Commented Jul 8, 2023 at 17:32

1 Answer 1


Apparently there was an update in ch340 drivers early in 2023 and it broke something for counterfeit ch340. Solution is using older version of the driver (and possibly disabling automatic updates for the drivers in the Windows).

Issue description and solution found on github:

Rollback to an older driver manually :

Unfortunately since the incompatible driver is delivered through windows update it is harder to keep an older driver installed :

Recommended : Block windows drivers update so the newest driver won't get installed automatically: https://www.makeuseof.com/windows-stop-automatic-driver-updates (note: while this is required to be able to install and keep the older ch340g driver but this will affect any of your future devices)

Reinstall an older driver here : 01/30/2019, 3.5.2019.1 CH341SER driver

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