Prusa error 13311 (I2C Send Failed) appears on the MK4 and its equivalents are #31311 on the CORE One, #35311 on the CORE One L, #26311 on the MK4S, #27311 on the MK3.9S, #21311 on the MK3.9, #28311 on the MK3.5S, #23311 on the MK3.5, and #12311 on the MINI. The Buddy board attempted to send data to a peripheral component over the I2C bus but the transmission failed.

What the Error Means

The I2C bus connects the Buddy board to various internal peripherals — including the display driver, accelerometer, and real-time clock in some configurations. An I2C Send Failed error means a data packet was written to the bus but no acknowledgment was received from the target peripheral. This is most commonly a transient timing glitch in the firmware that resolves on restart, but recurring failures can point to a loose connector on an I2C peripheral, an electrical fault on the bus, or a board-level hardware problem affecting the I2C controller.

Step-by-Step Fix

1. Restart the printer. A single occurrence of this error is nearly always transient — power off, wait 10 seconds, and power back on. Most users never see the error again.
2. Power cycle if a restart alone does not clear the error. Hold the power button to shut down, unplug the power cable from the wall, wait 30 seconds for capacitors to discharge, then reconnect and power on.
3. Check internal ribbon cables and connectors on the xBuddy board. With the printer powered off, open the electronics enclosure. Check that the ribbon cable to the LCD display and any other flat-flex connectors are fully inserted into their ZIF sockets without lifted corners.
4. Update firmware to the latest version. Navigate to prusa3d.com/drivers, download the firmware for your model, and install it via USB. Firmware updates often include I2C driver timing improvements.
5. Contact Prusa Support if the error is persistent. If the error returns every session or at a consistent point in the startup sequence, it suggests a hardware fault on the xBuddy board that requires professional evaluation.

Parts Required

• No replacement parts are typically required for this fix — basic tools only
• Replacement xBuddy board (if I2C fault is confirmed as hardware-level — contact Prusa Support first)

If restarting and updating firmware do not resolve the error, contact Prusa Support at help.prusa3d.com with a description of when the error occurs and how frequently.

Frequently asked questions

What does Prusa 13311 mean?

Prusa error 13311 (I2C Send Failed) appears on the MK4 and its equivalents are #31311 on the CORE One, #35311 on the CORE One L, #26311 on the MK4S, #27311 on the MK3.9S, #21311 on the MK3.9, #28311 on the MK3.5S, #23311 on the MK3.5, and #12311 on the MINI. The Buddy board attempted to send data to a peripheral component over the I2C bus but the transmission failed.

How do I fix Prusa 13311?

Prusa error 13311 means the Buddy board failed to send data over the I2C bus. Learn how to restart, check internal connectors, and determine if a board replacement is needed.