# Ender 3 s1 pro 'mcu errror'

**URL:** <https://klipper.discourse.group/t/ender-3-s1-pro-mcu-errror/18458>\
**Category:** General Discussion\
**Created:** [August 25, 2024, 12:38am UTC](https://klipper.discourse.group/t/ender-3-s1-pro-mcu-errror/18458 "2024-08-25T00:38:25Z")\
**Posts on this page:** 1\
**Showing post:** 6

<div class="post-metadata">

**Author:** ![DaVinci10](https://yyz2.discourse-cdn.com/free1/user_avatar/klipper.discourse.group/davinci10/32/2828_2.png) [@DaVinci10](https://klipper.discourse.group/u/DaVinci10)\
**Post date:** [August 25, 2024, 3:13am UTC](https://klipper.discourse.group/t/ender-3-s1-pro-mcu-errror/18458/6 "2024-08-25T03:13:46Z")

</div>

Have you read this one?

> [@Klipper cant connect to mcu](https://klipper.discourse.group/t/klipper-cant-connect-to-mcu/9987):
>
> Basic Information: Printer Model: ender 3 s1 pro MCU / Printerboard: STM32F401 [klippy.log](https://klipper.discourse.group/uploads/short-url/c55c59ldPrwzoOt0icV8UxrDCZx.log) (49.5 KB) Fill out above information and in all cases attach your klippy.log file. Describe your issue: …Hi Everyone. im relatively new to 3d printing and I am in the process of flashing klipper onto my ender 3 s1 pro I believe the flash went okay but i honestly don’t know how to tell, But when I connect my rpi to my printer mainsail it spits out an mcu error. I am extremely lost all help is much app…

in there I read

```Sineos
Aug 2023

fixed

@cbrew
Your error is:

mcu 'mcu': Unable to open serial port: [Errno 2] could not open port /dev/serial/by-id/usb-1a86_USB_Serial-if00-port0: [Errno 2] No such file or directory: '/dev/serial/by-id/usb-1a86_USB_Serial-if00-port0'
Check Debian Bullseye Bug causing Klipper to no longer find the printer board 54

```

It leads to this one..

> [@Debian 11 (Bullseye) udev bug - No board or serial found](https://klipper.discourse.group/t/debian-11-bullseye-udev-bug-no-board-or-serial-found/10711):
>
> Background In recent updates, Debian Bullseye (Debian 11) introduced a [bug in udev](https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1035094) that causes the command ls /dev/serial/by-id/\* to fail, because the bug prevents the creation of this device path. As of writing this, the bug remains unfixed in the regular Debian repositories, but it is already fixed in optional Debian repositories. How to Diagnose To check if the OS is affected by the bug, run: sudo apt -y update && sudo apt -y upgrade apt-cache policy udev If the command’s output display…

hope its that easy, alot of us users fell into the rights bug

on the Klipper discord they had pinned a script that did all the fixes. its pinned in the mainsail forum on klipper discord.

Fix for current by-id issue in debian updates

```auto
curl -sSL https://raw.githubusercontent.com/mainsail-crew/MainsailOS/develop/patches/udev-fix.sh | bash

```

I dont know if any of this is your issue, but like I said earlier. a bunch of us got hit with it.

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_[View the full topic](https://klipper.discourse.group/t/ender-3-s1-pro-mcu-errror/18458)._