does anyone know how to get out of this?

avrdude: ser_open(): can't open device "\.\COM4": Access is denied.

all of a sudden, pffffft!


I suggest you change the title of your question, if you expect help here.

avrdude: ser_open(): can't open device "\.\COM4": Access is denied.


thank you!

It appears that this has not changed the original title. I have also tried to change a tittle but failed.

Can someone please tell us how to do it so it changes the original thread title.


It's an error with your computer to Arduino serial connection. The COM4 is the port your Arduino is trying to connect to, but the computer can't sense the Arduino board you are trying to connect to your computer. So it can't upload the code. That's what it is.

Title all set - some things need a Moderator’s touch.

Also COM4 seems like an awfully low number, mine are much higher.

Com 4 seems low. It is a laptop, a PC version. I'm a Mac person. Is it possible that the firewall is not allowing access to the COM4 port? The drivers are updated, COM4 is selected in the tools, I've checked everything else that I can find resources on.

Thank you very much.

There is another way to fix. Look on the serial chip. Check to see what kind it is. If it is not a ATMEGA16U2 or 16U2 like normal, then you have to figure out what it is and install the driver needed. Also check if it is a CH340 or CH3406. If it is, then you have to install their drivers. Good Luck fixing! :)

If it was working, Did you leave a serial monitor out other piece of software connected to it open? Close that, then restart the ide.