Prusa error 13312 (I2C Send Busy) appears on the MK4. The Buddy board attempted to write data to the I2C bus but found the bus occupied, preventing the transmission from completing. This error is almost always a transient firmware timing event rather than a sign of hardware damage.

What the Error Means

The I2C bus is a shared communication channel — only one device can talk at a time, and each transmission requires the bus to be idle before it can begin. Under normal operation, the firmware manages I2C access to prevent collisions. An I2C Send Busy error means the firmware attempted a transmission but the bus was still busy from a previous operation, which is typically caused by a firmware scheduling issue rather than a wiring fault. It can also arise after a firmware update that changed I2C timing parameters, leaving residual state that requires a fresh boot to clear.

Step-by-Step Fix

1. Restart the printer. Power off, wait 10 seconds, and power back on. A single occurrence is almost never repeatable.
2. Update firmware to the latest version. I2C send busy errors are often addressed in firmware updates that refine the I2C bus arbitration and timeout handling. Download the latest firmware from prusa3d.com/drivers and install it via USB.
3. Inspect the xBuddy board connectors if the error recurs. Open the electronics enclosure and check that the LCD ribbon cable and any I2C peripheral connectors are seated fully. A partially inserted connector can cause unexpected bus state changes.
4. Contact Prusa Support if a firmware update does not resolve recurring errors. Provide the firmware version you updated from and to, and describe the frequency and context of the error.

Parts Required

• No replacement parts are typically required for this fix — basic tools only

If the error occurs repeatedly after updating to the latest firmware, contact Prusa Support at help.prusa3d.com for further evaluation.

Frequently asked questions

What does Prusa 13312 mean?

Prusa error 13312 (I2C Send Busy) appears on the MK4. The Buddy board attempted to write data to the I2C bus but found the bus occupied, preventing the transmission from completing. This error is almost always a transient firmware timing event rather than a sign of hardware damage.

How do I fix Prusa 13312?

Prusa error 13312 means the I2C bus was busy and could not complete a transmission. Learn how to restart and update firmware to clear this transient communication fault.