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System, Performance, and Service Errors

This page organizes content related to communication timeouts, MCU timer errors, host computer performance, firmware flashing, and Klipper service startup issues.

Homing Timeout Issues​

Error Message: Communication timeout during homing, Error during homing xxx during the homing process. Commonly seen in Z-axis homing scenarios with multiple MCUs.

Common Causes:

  • High load on the host computer, with KlipperScreen, camera streams, etc. running simultaneously.
  • Simultaneous movement of multiple axes during homing; high current drive signals couple into CAN/USB communication lines, causing interruptions.
  • Unstable communication responses from multiple MCUs.
  • Poor quality or improper routing of CAN/USB communication lines.

Solutions:

Power Off Operation

Before reorganizing CAN/USB wiring, checking shielding, or inspecting grounding, completely turn off the printer and disconnect the power supply. Do not modify the power ground wire, mains wiring, or internal power supply structure yourself.

  1. First, rule out electromagnetic interference: Check if CAN/USB wires are routed separately from motor wires and heater wires. Refer to the interference troubleshooting steps in CAN Network Configuration and ID Search.
  2. Try adjusting the TRSYNC_TIMEOUT parameter or temporarily disable KlipperScreen. See Homing Timeout Issues.
  3. Check the machine's grounding and shield grounding.

MCU 'mcu' shutdown: Stepper too far in past​

Error Message: A stepper event has exceeded the time range the MCU can handle, causing the printer to enter a shutdown state.

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Reference Scenario: This error is not necessarily caused by bed mesh configuration. The actual cause needs to be determined by analyzing klippy.log and the current operation. During multi-point probing, if the probe_count in [bed_mesh] is set too high, especially in combination with a high mesh_pps, it can generate excessively dense mesh data, increasing host computer calculation and motion planning pressure.

Solutions:

  1. If the error occurs during multi-point probing, first reduce the probe_count in [bed_mesh], e.g., to 7,7 or 9,9.
  2. If a high mesh_pps is configured, reduce or remove it, e.g., set mesh_pps: 2,2.
  3. After saving the configuration and restarting Klipper, re-execute the operation that triggered the error.
  4. If the error persists, continue checking host computer load, print speed, acceleration, communication quality, and the currently executing macro or G-code.

Related configuration reference: Macros, Common Debugging Directives.

MCU 'mcu' shutdown: Timer too close​

Error Message: The MCU timer is too close, causing a system timeout.

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Error Cause: High load on the microcontroller unit (MCU), slow response from the host computer, excessive print speed, excessively high micro-stepping, system clock synchronization interference, or interference on the MCU communication line can all trigger this issue.

Solutions:

  1. Reduce stepper motor micro-stepping to decrease MCU pulse processing load.
  2. Lower print speed and acceleration and observe if the problem resolves.
  3. Check host computer load, power supply, and USB/CAN communication quality.
  4. After powering off, check if the communication lines between the MCU and the host computer are routed near motor wires, heater wires, heat bed wires, or power wires. Re-route or replace with shielded communication cables if necessary.
  5. When checking machine grounding, only verify the manufacturer-provided grounding points and outlet status. Do not disassemble the power supply or modify the mains ground wire yourself.
  6. If the problem occurs during the homing phase, refer to Homing Timeout Issues.
  7. If the problem persists, consider re-flashing the host computer system or firmware.

Related configuration reference: Common Debugging Directives, Homing and Direction Calibration Guide.

Rescheduled timer in the past​

Error Message: Log shows Rescheduled timer in the past or similar warnings.

Error Cause: Host computer system clock issues or high CPU load causing the scheduled task to execute later than planned.

Solutions:

  1. If NTP synchronization is enabled, temporarily disable it for testing.
  2. Reduce the load of other services running on the host computer, such as closing unnecessary web interfaces or camera streams.
  3. If running in a virtual machine, consider migrating to a physical machine or using a more stable clock source.
  4. Check host computer CPU usage: use htop to see if the klippy process has abnormally high CPU usage.

Related configuration reference: Common Debugging Directives.

Internal error on command​

Error Message: Internal error on command:"XXX", Klipper enters a shutdown state.

Common Causes:

  • A macro or G-code command triggers a Python exception inside Klipper.
  • Incorrect macro references or Jinja2 template syntax errors in the configuration file.
  • Klipper version incompatibility with the configuration file format.
  • G-code filenames containing special characters causing encoding errors.

Solutions:

  1. Check klippy.log for the full Python Traceback below the Internal error message.
  2. Based on the Traceback, identify which configuration file or macro has the issue.
  3. Common causes include Jinja2 template syntax errors in [gcode_macro], missing [respond] configuration, or incorrect [virtual_sdcard] path.
  4. If the error relates to SDCARD_PRINT_FILE and shows ascii codec can't decode, rename the G-code file to use only English letters, numbers, underscores, or hyphens.

Related configuration reference: Macros, Configuration Modification Notes.

Unable to open file​

Error Message: Unable to open file when trying to print a file.

Common Causes:

  • The G-code file does not exist, its name was changed, or the upload was incomplete.
  • The [virtual_sdcard] path points to the wrong directory.
  • File permission issue preventing the Klipper user from reading the file.
  • The filename contains special characters causing path processing errors in certain frontends or systems.

Solutions:

  1. Re-upload the G-code file via the web interface and confirm the filename matches the print command.
  2. Verify that the [virtual_sdcard] path points to the actual G-code storage directory.
  3. Check directory permissions: ls -la ~/printer_data/gcodes/.
  4. Rename the file using only English letters, numbers, underscores, or hyphens and try again.

Related configuration reference: Configuration Modification Notes.

MCU CRC does not match config / Can not update MCU config​

Error Message: MCU 'xxx' CRC does not match config, Can not update MCU 'xxx' config as it is shutdown, Unable to configure MCU 'xxx'.

Solutions:

  1. Execute FIRMWARE_RESTART. If necessary, power off the entire machine for 10 seconds, then power it back on.
  2. Look in klippy.log for the first error that occurred earlier. Address the root cause that led to the shutdown first.
  3. For multi-MCU machines, check the USB ID or CAN UUID for each [mcu] and [mcu xxx] individually.
  4. If you just updated Klipper, recompile and flash all MCU firmwares.

Shutdown due to M112 command / webhooks request​

Error Message: Shutdown due to M112 command or Shutdown due to webhooks request.

Solutions:

  1. Confirm if the emergency stop was triggered manually. If so, rule out the risk and execute FIRMWARE_RESTART.
  2. Search for M112, action_emergency_stop, and emergency_stop in any custom macros.
  3. Check if the web frontend, remote control plugins, or automation scripts are inadvertently triggering the emergency stop interface.

Error Message: No obvious error, but intermittent pauses or extrusion inconsistencies occur during printing.

Solutions:

  1. Reduce print speed and acceleration.
  2. Disable unnecessary web services, camera streams, etc., on the host computer.
  3. Reduce probe_count and mesh_pps in [bed_mesh].
  4. If the host computer's performance is genuinely insufficient, consider upgrading to a more capable host.

Klipper Repeatedly Restarting (Klippy not connected Flashing Repeatedly)​

Error Message: Mainsail/Fluidd shows Klippy not connected appearing repeatedly. Klipper keeps restarting automatically, exiting within seconds each time. Logs may show Klipper restarting too fast or each klippy.log cycle is very short.

Troubleshooting Steps:

  1. First, check the end of the log file to identify the reason for the last exit: 
    tail -100 ~/printer_data/logs/klippy.log
  2. If the end of the log file contains a Python Traceback, it indicates a crash due to a configuration parsing error or internal exception.
  3. Do not rely solely on Klipper restarting too fast as the root cause. This is often just the result of systemd repeatedly failing to restart the service. Prioritize fixing the first real error shown in klippy.log.
  4. If the log ends with MCU Protocol error, Unknown command, etc., it means the firmware version is mismatched. Recompile and reflash the MCU firmware.
  5. If the log is very short with no obvious error, try using a minimal configuration with a binary search approach to isolate the problem.
  6. Check for circular references in included files.
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