<p>The issue sometimes persisted on only 1/2 machines running octoprint. I found this <a href="https://github.com/OctoPrint/OctoPrint/issues/3627#issuecomment-654236051" rel="nofollow noreferrer">comment</a> regarding the &quot;Serial Port&quot; and &quot;Baudrate&quot; settings, I noticed both were set to AUTO on the server with a working connection, but were set to fixed non-AUTO values on the failing server. Setting both to AUTO resolved the issue.</p>
<p><a href="https://i.sstatic.net/OUJdzz18.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/OUJdzz18.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2024-06-23T13:08:15.723Z
This is your second "Answer". If you would like to add/change any information in an existing answer, please use the [Edit] feature below the answer to make the adjustments.
agarza
CC BY-SA 4.0
2024-06-23T15:35:37.997Z
These are two separate answers.
user84207
CC BY-SA 4.0
2024-06-23T12:11:15.430Z
2024-06-23T12:11:15.430Z
user84207
<p>The issue appears to have spontaneously resolved itself after re-opening the bottom lid of the board, and after rearranging some of the cables on the table. Perhaps there was some type of electrical interference causing problems with the USB cable serial connection.</p>

CC BY-SA 4.0
2024-06-22T03:46:52.710Z
2024-06-22T03:46:52.710Z
user84207
<p>I'm suddenly unable to connect to my Creality Ender 3 Pro 3D printer (CrealityV4.2.2) via the USB/serial port using Octoprint. Here are some of the logs from Octoprint:</p>
<pre><code>2024-06-21 19:37:05,147 - octoprint.util.comm - INFO - Changing monitoring state from &quot;Offline&quot; to &quot;Detecting serial connection&quot;
2024-06-21 19:37:05,153 - octoprint.util.comm - INFO - Serial detection: Performing autodetection with 10 port/baudrate candidates: /dev/ttyUSB5@115200, /dev/ttyUSB5@250000, /dev/ttyS0@115200, /dev/ttyS0@250000, /dev/ttyS3@115200, /dev/ttyS3@250000, /dev/ttyS2@115200, /dev/ttyS2@250000, /dev/ttyS1@115200, /dev/ttyS1@250000
2024-06-21 19:37:05,153 - octoprint.util.comm - INFO - Serial detection: Trying port /dev/ttyUSB5, baudrate 115200
2024-06-21 19:37:05,154 - octoprint.util.comm - INFO - Connecting to port /dev/ttyUSB5, baudrate 115200
2024-06-21 19:37:05,202 - octoprint.util.comm - INFO - Serial detection: Handshake attempt #1 with timeout 2.0s
2024-06-21 19:37:05,205 - octoprint.util.comm - INFO - M110 detected, setting current line number to 0
2024-06-21 19:37:05,910 - octoprint.server - INFO - Autorefresh of serial port list stopped
2024-06-21 19:37:07,212 - octoprint.util.comm - INFO - Serial detection: Handshake attempt #2 with timeout 2.0s
2024-06-21 19:37:07,213 - octoprint.util.comm - INFO - M110 detected, setting current line number to 0
2024-06-21 19:37:07,218 - octoprint.util.comm - ERROR - Unexpected error while reading from serial port
Traceback (most recent call last):
  File &quot;/home/ealfonso/.venv/lib/python3.11/site-packages/octoprint/util/comm.py&quot;, line 4081, in _readline
    ret = self._serial.readline()
          ^^^^^^^^^^^^^^^^^^^^^^^
  File &quot;/home/ealfonso/.venv/lib/python3.11/site-packages/octoprint/util/comm.py&quot;, line 6832, in readline
    c = self.read(1)
        ^^^^^^^^^^^^
  File &quot;/home/ealfonso/.venv/lib/python3.11/site-packages/serial/serialposix.py&quot;, line 595, in read
    raise SerialException(
serial.serialutil.SerialException: device reports readiness to read but returned no data (device disconnected or multiple access on port?)
2024-06-21 19:37:07,221 - octoprint.util.comm - ERROR - Please see https://faq.octoprint.org/serialerror for possible reasons of this.
2024-06-21 19:37:07,223 - octoprint.util.comm - INFO - Changing monitoring state from &quot;Detecting serial connection&quot; to &quot;Offline after error&quot;
2024-06-21 19:37:07,225 - octoprint.server - INFO - Starting autorefresh of serial port list
2024-06-21 19:37:07,227 - octoprint.plugins.action_command_notification - INFO - Notifications cleared
2024-06-21 19:46:36,410 - octoprint.server.heartbeat - INFO - Server heartbeat &lt;3
2024-06-21 20:01:36,410 - octoprint.server.heartbeat - INFO - Server heartbeat &lt;3
</code></pre>
<p>Some of the recent changes or events that may be relevant:</p>
<ol>
<li>I recently installed a Z probe sensor like BLTouch or CRTouch</li>
<li>I put silicone around the 3+2 pins before closing the bottom lid</li>
<li>Right before the connection failures, I received a &quot;M112 shutdown&quot; blue screen of death after attempting to run the command <code>M420 S1</code> from Octoprint</li>
<li>The printer works fine from an SD card</li>
<li>I tried blocking the USB 5 V with tape as suggested in <a href="https://community.octoprint.org/t/octoprint-randomly-loses-connection-to-the-printer-with-a-serialexception/228" rel="nofollow noreferrer">OctoPrint randomly loses connection to the printer with a &quot;SerialException&quot;</a> but this didn't help</li>
<li>I tried using different cables but this didn't help
7 I tried re-flashing the Marlin firmware (bugfix-2.1.x) via the SD card, this did work but did not help the connection issue</li>
<li>I tried connecting the printer to different machines running Octoprint, all Octoprint instances report the same serial connection error</li>
</ol>
<p>How can I debug this connection issue? I'm considering ordering a replacement board but I'd like to be able to troubleshoot the issue.</p>

<creality-ender-3><marlin><usb>
Device reports readiness to read but returned no data
user84207
# Device reports readiness to read but returned no data

(Asked by: username_0 on 2024-06-22)

I'm suddenly unable to connect to my Creality Ender 3 Pro 3D printer (CrealityV4.2.2) via the USB/serial port using Octoprint. Here are some of the logs from Octoprint:
2024-06-21 19:37:05,147 - octoprint.util.comm - INFO - Changing monitoring state from "Offline" to "Detecting serial connection"
2024-06-21 19:37:05,153 - octoprint.util.comm - INFO - Serial detection: Performing autodetection with 10 port/baudrate candidates: /dev/ttyUSB5@115200, /dev/ttyUSB5@250000, /dev/ttyS0@115200, /dev/ttyS0@250000, /dev/ttyS3@115200, /dev/ttyS3@250000, /dev/ttyS2@115200, /dev/ttyS2@250000, /dev/ttyS1@115200, /dev/ttyS1@250000
2024-06-21 19:37:05,153 - octoprint.util.comm - INFO - Serial detection: Trying port /dev/ttyUSB5, baudrate 115200
2024-06-21 19:37:05,154 - octoprint.util.comm - INFO - Connecting to port /dev/ttyUSB5, baudrate 115200
2024-06-21 19:37:05,202 - octoprint.util.comm - INFO - Serial detection: Handshake attempt #1 with timeout 2.0s
2024-06-21 19:37:05,205 - octoprint.util.comm - INFO - M110 detected, setting current line number to 0
2024-06-21 19:37:05,910 - octoprint.server - INFO - Autorefresh of serial port list stopped
2024-06-21 19:37:07,212 - octoprint.util.comm - INFO - Serial detection: Handshake attempt #2 with timeout 2.0s
2024-06-21 19:37:07,213 - octoprint.util.comm - INFO - M110 detected, setting current line number to 0
2024-06-21 19:37:07,218 - octoprint.util.comm - ERROR - Unexpected error while reading from serial port
Traceback (most recent call last):
  File "/home/ealfonso/.venv/lib/python3.11/site-packages/octoprint/util/comm.py", line 4081, in _readline
    ret = self._serial.readline()
          ^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/ealfonso/.venv/lib/python3.11/site-packages/octoprint/util/comm.py", line 6832, in readline
    c = self.read(1)
        ^^^^^^^^^^^^
  File "/home/ealfonso/.venv/lib/python3.11/site-packages/serial/serialposix.py", line 595, in read
    raise SerialException(
serial.serialutil.SerialException: device reports readiness to read but returned no data (device disconnected or multiple access on port?)
2024-06-21 19:37:07,221 - octoprint.util.comm - ERROR - Please see https://faq.octoprint.org/serialerror for possible reasons of this.
2024-06-21 19:37:07,223 - octoprint.util.comm - INFO - Changing monitoring state from "Detecting serial connection" to "Offline after error"
2024-06-21 19:37:07,225 - octoprint.server - INFO - Starting autorefresh of serial port list
2024-06-21 19:37:07,227 - octoprint.plugins.action_command_notification - INFO - Notifications cleared
2024-06-21 19:46:36,410 - octoprint.server.heartbeat - INFO - Server heartbeat <3
2024-06-21 20:01:36,410 - octoprint.server.heartbeat - INFO - Server heartbeat <3

Some of the recent changes or events that may be relevant:

I recently installed a Z probe sensor like BLTouch or CRTouch
I put silicone around the 3+2 pins before closing the bottom lid
Right before the connection failures, I received a "M112 shutdown" blue screen of death after attempting to run the command M420 S1 from Octoprint
The printer works fine from an SD card
I tried blocking the USB 5 V with tape as suggested in OctoPrint randomly loses connection to the printer with a "SerialException" but this didn't help
I tried using different cables but this didn't help
7 I tried re-flashing the Marlin firmware (bugfix-2.1.x) via the SD card, this did work but did not help the connection issue
I tried connecting the printer to different machines running Octoprint, all Octoprint instances report the same serial connection error

How can I debug this connection issue? I'm considering ordering a replacement board but I'd like to be able to troubleshoot the issue.

**Tags:** creality-ender-3, marlin, usb

---

## 2 answers

### Answer by username_0 on 2024-06-23. Score: 1

The issue sometimes persisted on only 1/2 machines running octoprint. I found this [comment](https://github.com/OctoPrint/OctoPrint/issues/3627#issuecomment-654236051) regarding the "Serial Port" and "Baudrate" settings, I noticed both were set to AUTO on the server with a working connection, but were set to fixed non-AUTO values on the failing server. Setting both to AUTO resolved the issue.

[![enter image description here](https://i.sstatic.net/OUJdzz18.png)](https://i.sstatic.net/OUJdzz18.png)

> **Comments:**
> **username_1**: This is your second "Answer". If you would like to add/change any information in an existing answer, please use the [Edit] feature below the answer to make the adjustments.  
> **username_0**: These are two separate answers.  

---

### Answer by username_0 on 2024-06-22. Score: 0

The issue appears to have spontaneously resolved itself after re-opening the bottom lid of the board, and after rearranging some of the cables on the table. Perhaps there was some type of electrical interference causing problems with the USB cable serial connection.


---

