I am unable to upload a sketch to a Nano

Development Tools Uploading
1

I am attempting to upload a sketch to a Nano but receive the following error messages:

Error: cannot open port \.\COM4: Access is denied.
Error: unable to open port COM4 for programmer arduino
Failed uploading: uploading error: exit status 1

The sketch works perfectly well using an UNO R3.
I have tried different Nanos, ports and cables and I have uninstalled the CH340 without success.

Help please.

2

Hi @Spatourer. There is a known bug in Arduino IDE 2.x that can cause uploads to fail with this "Access is denied" error if you try uploading to a board like the official Nano that uses an FTDI FT232R USB chip while the Arduino IDE Serial Monitor or Serial Plotter is open.

A port can only be used by one process at a time, so Arduino IDE must automatically close the port in Serial Monitor and Serial Plotter during an upload, automatically opening it again after. For some reason, that juggling of the port control is not working with boards that have the FTDI USB chip.

If that bug is the cause of the problem you are having, the workaround will be to manually close the port in Serial Monitor/Serial Plotter before doing an upload. Please give that a try and then let me know if you still have the error while uploading:

Serial Monitor

  1. Click the X icon on the "Serial Monitor" tab in the bottom panel of the Arduino IDE window to close the tab:
    image
    image405×345 38 KB
  2. Upload the sketch.
  3. Open Serial Monitor again if needed (by clicking the icon on the IDE toolbar or the Tools > Serial Monitor menu item) after the upload is finished.

Serial Plotter

If you have the "Serial Plotter" window open, the procedure is a bit different from closing the Serial Monitor connection:

  1. Close the "Serial Plotter" window.
  2. If the "Serial Monitor" view is not already open, select Tools > Serial Monitor from the Arduino IDE menus to open it.
    ⓘ We must do an open/close cycle on Serial Monitor as a workaround for a bug in Serial Plotter
  3. Click the X icon on the "Serial Monitor" tab in the bottom panel of the Arduino IDE window to close the tab:
    image
    image405×345 38 KB
  4. Upload the sketch.
  5. Open Serial Monitor and/or Serial Plotter again if needed after the upload is finished.

Please let me know if you have any questions or problems while following those instructions.

3

Works a treat!
Much appreciated.

4

You are welcome. I'm glad it is working now.

Regards, Per