One of two boards, cannot update firmware

Official Hardware UNO Family UNO R4 WiFi
1

I have two Arduino UNO R4 WiFi boards. Both operate perfectly, zero issues uploading my application (I use the same app on both with different PIN configuration data on each). Never any issues with the IDE identifying the boards or doing uploads.

On one of them (the problem unit), when my webserver starts I get the "Please update the firmware" warning in the Serial Monitor. That's the reason I'm trying to update the firmware.

Now, I have read dozens of similar posts on this and other forums. None of the solutions are working for me.

I finally captured a log (running the IDE in the terminal - I'm on Linux) showing the errors.

My testing routing today (where I captured the errors) was this:

  • In the IDE, turned off the serial monitor
  • Shut down the PC
  • Removed all USB devices including the Arduino
  • Restarted the PC
  • Plugged in (only) the Arduino
  • Double-pressed the reset button
  • Ran a terminal session and started the IDE (Appimage version 2.3.10)
  • Loaded the basic example (the one that simply fades the LED in & out)
  • Ensured the serial monitor was not open
  • Attempted the firmware update. It successfully recognized my board and the correct (only) USB port
  • Started the update. Saw what I've been seeing every time; the lights flash fast for a few seconds, then a single Tx flash followed by a single Rx flash. A few seconds later, I get the failure message.

Here's what the terminal session captured:

2026-06-16T09:50:15.757Z fwuploader ERROR Error: Error executing /tmp/.mount_arduinDrKX7Y/resources/app/lib/backend/resources/arduino-fwuploader firmware flash --fqbn arduino:renesas_uno:unor4wifi --address /dev/ttyACM0 --module ESP32-S3@0.6.0: [2026-06-16T09:50:07Z INFO ] 🚀 A new version of espflash is available: v4.4.0
[2026-06-16T09:50:07Z INFO ] Serial port: '/dev/ttyACM0'
[2026-06-16T09:50:07Z INFO ] Connecting...
[2026-06-16T09:50:07Z INFO ] Unable to connect, retrying with extra delay...
[2026-06-16T09:50:07Z INFO ] Unable to connect, retrying with default delay...
[2026-06-16T09:50:07Z INFO ] Unable to connect, retrying with extra delay...
[2026-06-16T09:50:07Z INFO ] Unable to connect, retrying with default delay...
[2026-06-16T09:50:07Z INFO ] Unable to connect, retrying with extra delay...
[2026-06-16T09:50:07Z INFO ] Unable to connect, retrying with default delay...
[2026-06-16T09:50:07Z INFO ] Unable to connect, retrying with extra delay...
Error: espflash::connection_failed

  × Error while connecting to device
  ╰─▶ Failed to connect to the device
  help: Ensure that the device is connected and the reset and boot pins are
        not being held down

Error: exit status 1
Error: reboot mode: upload commands sketch: setting DTR to OFF
Error: reboot mode: upload commands sketch: setting DTR to OFF
Error: reboot mode: upload commands sketch: setting DTR to OFF
Error: reboot mode: upload commands sketch: setting DTR to OFF
Error: reboot mode: upload commands sketch: setting DTR to OFF
Error: reboot mode: upload commands sketch: setting DTR to OFF
Error: reboot mode: upload commands sketch: setting DTR to OFF
Error: reboot mode: upload commands sketch: setting DTR to OFF
    at ChildProcess.<anonymous> (/tmp/.mount_arduinDrKX7Y/resources/app/lib/backend/main.js:2:667496)
    at ChildProcess.emit (node:events:519:28)
    at ChildProcess._handle.onexit (node:internal/child_process:294:12)

I'm not sure where to go next. Based on what I've read online, I don't seem to have the bridge-software-missing issue (I say that, because when I power cycle the Arduino and plug it back in, the IDE never has a problem identifying it as the UNO R4 WiFi and on the correct port). The instructions state the if the IDE doesn't recognize the board, then you need to run the process to restore the bridge software. But I don't have that issue.

Other info:

  • I have tried this on 3 different PCs. My main Linux development machine, and 2nd Linux machine, and a Windows 11 machine. Same results every time.
  • I have tried 3 different cables, all of which allow uploading to the device perfectly.

Any help would be greatly appreciated!

2

Did you try shorting the ESP Download pin to GND while resetting/powering up the board? The short/link can be removed after power up. I think that's needed to get the board into ESP download mode so that the firmware can be uploaded.

3

I did not, but the only instructions I ran across saying to do that were in reference to if the Arduino had had a sketch uploaded to it, after a failed firmware update attempt, which wipes out the bridge software. The indicator of that is that the IDE cannot identify the board as a UNO R4 Wifi. My IDE never has any problem identifying it as such.

4

Firmware upgrade procedure:

https://support.arduino.cc/hc/en-us/articles/16379769332892-Restore-the-USB-connectivity-firmware-on-UNO-R4-WiFi-with-espflash

There is also this thread with similar error messages to the ones you posted:

https://forum.arduino.cc/t/arduino-uno-r4-wifi-firmware/1355018/3

But yes, point taken that your board is still being identified.

5

Yeah, this:

You may want to use this procedure if:
Your UNO R4 WiFi is detected as a generic ESP32 board by Arduino IDE or Arduino Cloud.
Your UNO R4 WiFi isn’t detected as any board by Arduino IDE or Arduino Cloud, despite being connected to your computer with a working data USB cable.

Is why I hadn't tried this procedure before. The way that article is worded, there's no need for me to do that (or at least that's how I interpreted it). And I had already read over the 2nd link's article, but again that seems to be needed only if the ESP-2 module needs to be reprogrammed (which, again, supposedly is only when the IDE can't identify the board at all, or identifies it as some generic board other than the UNO R4 Wifi).

Appreciate the help.