The Original Prusa MK4/MK3.9 displays the message: "Failed to home the extruder in X-axis, make sure there is no obstacle on X-axis".
Error name: Homing error X
Error code: #13304 (MK4) #21304 (MK3.9)
The error is most likely caused by a bad movement of the print head along the X-axis.
Make sure there are no obstructions in the path of the X-axis. For example, there might be a piece of filament stuck around the belt, or on a smooth rod, from a previous print.
Check the X-axis belt tension and adjust it, following our dedicated article on belt adjustment.
The X-axis motor pulley is attached to the X-axis motor shaft. The motor shaft has one flat side. The pulley has two set screws: ensure that one of the two set screws is aligned with the flat part of the motor shaft. Make sure the other set screw is also tightened, not excessively, and that there is a small space between the pulley and the motor.
An over-tightened or loose X-carriage and X-carriage-clip assembly might cause the error. If none of the previous steps resolved the issue, refer to our assembly manual to see the assembly of the X-carriage and X-carriage-clip.