Programs will not upload to Zumo 32u4

I was uploading a program to my zumo 32u4 and I accidentally disconnected it early. Now I can’t upload anything too it. Aruduino software shows an uploading progress bar but then the bar disappears and I’m not even given a message that the upload failed. Also, the red led that would always turn on when the zumo was powered up and flash when a program was being uploaded doesn’t seem to turn on in either case. Is there a simple fix or did I somehow damage my zumo.


I am sorry you are having issues re-programming your Zumo 32U4 board. It sounds like the app on your Zumo 32U4 was not fully uploaded, so it is malfunctioning. Can you follow the setups in the “Reviving an unresponsive Zumo 32U4” section in its user’s guide and try uploading your program again to see if that fixes the problem?

- Amanda


I’d advise to try double-reset to get into bootloader mode and try upload then.
Try it multiple times - should start working at some point.

Also try resetting board just after upload starts.

And check if your Arduino IDE recognizes proper COM port - it happened to me that after Zumo / A-Star got unresponsive, COM port changed on my Arduino IDE and I had to edit preferences.txt directly to bring it back to proper value.

No worries - your Zumo will be OK :wink:


Hi there. I have a few dozens Zumo32U4 which I use for education porpuses.
They are becoming more and more often unresponsive. This is very annoying.
Is there any plans from Pololu to solve this definitely? Maybe a new firmware…


In cases like the original poster’s, a Zumo can become unresponsive if a bad program is loaded onto it or if a program does not get fully copied during uploading (possibly when the upload is interrupted). If that is what you are observing, it is not a bug with the Zumo bootloader, and there is no firmware solution for preventing this kind of thing.

If you tell me more about the issues and how you are using the Zumo robots, I would be happy to help you troubleshoot. When do the problems happen? Are you able to get them back to normal by following the instructions for reviving an unresponsive Zumo 32U4? What program are you loading on the Zumos? Could you post a complete copy of it here?

- Amanda

Hi Amanda.
Thank you for your reply.
Yes, I am able to get them back by following the instructions provided in the User Guide.

It happens to me with different groups of students. I cannot identify any particular sketch that causes it. I think it also happens with sample code provided with the library.

It sounds like the problem happens after uploading a sketch to the Zumo 32U4. We have tested all of the example sketches for the Zumo 32U4 and have not heard of others having problems programming their Zumo 32U4 robots such that they are becoming increasingly unresponsive. As I said in my previous post, the Zumo can become unresponsive due to a bad program upload or when the upload is interrupted (e.g. USB connection is removed during programming). However, without any specific details, it is hard to pinpoint what might be causing the issue and fix it.

How often do the Zumos get in an unresponsive state?

When the problem happens again, I suggest having the students document their steps during the sketch upload (e.g. disconnected USB cable from Zumo unit before the Arduino IDE displayed “Done uploading”) and saving a copy of that sketch file, even if it is an example from the Zumo 32U4 library. Then post those steps and sketch file here.

- Amanda

As we are getting to the end of the semester, we have less cases of unresponsive Zumo32U4. The cause of previous problem seems to have been interrupted upload of sketches.
Thank you!

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