Prusa Crash Detected on Y Axis — Causes & Fix

What Does This Error Mean?

Crash Detected on the Y axis means the bed (which moves on Y) skipped steps — the stepper motor commanded movement but didn't actually move that far.
Causes are usually mechanical: belt too loose, motor current too low, debris under the bed, or something physically blocking the bed's travel.
Run an XYZ calibration after fixing the cause.

Affected Models

Prusa MK3S+
Prusa MK4
Prusa MK3.5

Common Causes

Y-axis belt too loose — slips on the pulley under load
Y motor current set too low in firmware
Debris caught under the bed blocking smooth travel
Bed wires snagged on the frame at the back
Worn Y-axis bearings — bed binds at certain positions

How to Fix It

Move the bed by hand and feel for resistance.

Power off the printer.
Push the bed slowly forward and backward by hand.
It should glide smoothly with light resistance from the belt.
Sticky spots, grinding, or sudden stops are signs of mechanical issues that caused the crash.
Check the Y-axis belt tension.

The belt runs along the bottom of the printer.
It should be taut enough that pinching it pulls about 5mm before snapping back.
If it's loose enough to push it side-to-side easily, retension it — Prusa has model-specific tensioning instructions.
Look under the bed for debris.

Lift the bed if you can or shine a torch underneath.
Stray bits of filament, lost screws, or tools left in the wrong place can jam the Y-axis travel.
Clear anything you find.
Check the bed wires routing.

The thick cable bundle at the back of the bed flexes every time the bed moves.
If it's been routed badly or the strain relief has come loose, it can snag on the frame at certain bed positions.
That snag is what causes the crash.
Reroute the cable so it flexes freely throughout the full Y travel.
Run XYZ calibration.

From the LCD menu, run the full XYZ calibration.
This re-homes the printer and reverifies the geometry.
If calibration completes without crashing, you've fixed the issue.
If it crashes again on Y, the bearings may be worn — replacement is a 30-minute job with new linear bearings.

Frequently Asked Questions

Can I just disable crash detection?

Yes, but you shouldn't.
Crash detection saves prints when the Y axis is about to fail — without it, missed steps shift the print and you get a wreck on the bed.
If crashes are frequent enough that you want to disable detection, the underlying mechanical issue should be fixed instead.

What's the difference between a Y crash and an X crash?

X crashes are the toolhead missing steps; Y crashes are the bed missing steps.
Both come from similar causes — loose belts, low current, mechanical drag — but the troubleshooting is on different axes.
The MMU and toolhead cable on a multi-material setup can also pull on X movement and cause X-specific crashes.