usi3d

Klipper: board communication errors (Lost communication with MCU, MCU shutdown, Move out of range)

Guide based on the manufacturer's official documentation; usi3d has not yet verified it on a machine.

Technology: FDM · Symptoms: The printer shows an error code or message, Problems after a firmware update · Updated on 9 October 2026

Symptom

The print stops and Klipper shows an error: “Lost communication with MCU”, the board (MCU) goes into a shutdown state, or “Move out of range” appears, sometimes right after homing. In some cases the computer running Klipper (for example a Raspberry Pi) reboots during the print.

Likely causes, from most to least likely

  1. Faults in the USB link between the computer and the board: a poor quality cable or loose plugs.
  2. Poor power: an insufficient Raspberry Pi supply (under voltage warnings) or an overloaded printer supply, which can reset the board's USB chip.
  3. Pinched or frayed motor, heater or other wires that, as they move, lose contact, short briefly or create electrical noise.
  4. The printer's and the computer's 5 V supplies are mixed: the board powers on with just the USB cable.
  5. A system program interfering with the serial port, such as ModemManager on some Linux distributions.
  6. After a G28, the toolhead ends up outside the valid range and the next move gives “Move out of range”.

Checks to tell which one it is

  • Save the klippy.log (at /tmp/klippy.log) before restarting: Klipper's logextract.py script extracts the MCU shutdown information from it.
  • Check whether the error coincides with print head or bed movement: that points to a damaged wire.
  • Check whether the Raspberry Pi reports under voltage warnings.
  • With the printer off, connect only the USB: if the board powers on, the 5 V supplies are mixed.
  • If the error is “Move out of range” right after homing, check what your start macro does after the G28.
  • If you've just updated Klipper and it warns that the board must be reflashed, the computer and board versions don't match.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

  1. Fix the cause and clear the error

    Klipper stops the printer on purpose rather than carry on with a fault; in the shutdown state, the board turns off heaters and motors. Once you've fixed the cause, send FIRMWARE_RESTART, which clears the board's error state (RESTART doesn't).

    Check: Klipper is ready again and the printer works.

    If that does not fix it: Check the USB cable.

  2. Replace the USB cable and secure the plugs

    Use a good quality USB cable between the computer and the board and check that both ends are fully seated.

    Check: The communication errors stop appearing.

    If that does not fix it: Check the power supply.

  3. Fix the power supply

    Use a good power supply and cable for the Raspberry Pi, fix any under voltage warning, and check that the printer's power supply isn't overloaded.

    Check: No under voltage warnings and the board doesn't reset.

    If that does not fix it: Check the printer wiring.

  4. Check the printer wiring

    Turn off and unplug the printer. Inspect the motor, heater and sensor wires along their paths: no pinches, no cuts, and properly secured.

    Check: The errors don't appear when the print head or bed moves.

    If that does not fix it: Check the 5 V supplies.

  5. Don't mix the 5 V supplies

    If the board powers on with just the USB, configure it to take power from a single source, following your board's manual.

    Check: The board only powers on from the printer's power supply.

    If that does not fix it: Check the operating system.

  6. Disable ModemManager if your system uses it

    If you installed Klipper on a Linux distribution that enables ModemManager (or a similar package) and you see random communication errors, disable that package.

    Check: The random disconnections stop.

    If that does not fix it: Check the klippy.log with logextract.py to see what happened before the shutdown.

  7. “Move out of range” after homing

    Change your start macro or start G-code to move the toolhead to a valid position right after the G28.

    Check: Starting a print no longer gives this error.

    If that does not fix it: Check the klippy.log to see which move fails.

  8. After updating: flash the board too

    If Klipper warns that the MCU must be reflashed, build and flash its firmware (make menuconfig, make clean, make and make flash) and review the configuration changes document. RESTART and FIRMWARE_RESTART don't load new software.

    Check: Klipper starts without version warnings.

    If that does not fix it: Review printer.cfg against the configuration changes document.

Prevention

  • Use good quality USB cables and power supplies.
  • Secure and route cables so they don't get pinched or frayed by movement.
  • Before updating Klipper, read the configuration changes document.

Still not fixed?

Tell usi3d's AI about your case: choose your printer, describe what you see and add photos if you like. It proposes checks step by step, with their sources.

Tell the AI about your case

Printers it applies to

Any FDM (filament) 3D printer, from any brand.

Official sources

This guide summarises the official documentation linked here:

This guide is general information: usi3d has summarised it from the official documentation linked here, and it may not match your model, its version or its firmware. If in doubt, follow the manual and the support of your printer's manufacturer. You decide what you do with your machine, and working on it may affect its warranty.

Related guides