Prusa error 13803 (G-Code Not Fully Compatible) appears on the MK4 and its equivalents are #31803 on the CORE One, #26803 on the MK4S, #27803 on the MK3.9S, #28803 on the MK3.5S, #21803 on the MK3.9, #23803 on the MK3.5, #17803 on the XL, and #12803 on the MINI. The print file contains G-code that was sliced for a hardware configuration that does not fully match what the printer has installed — most often a nozzle diameter mismatch.

What the Error Means

PrusaSlicer embeds metadata in G-code files that describes the printer model, nozzle size, and hardware configuration the file was sliced for. When the printer loads a file, it compares this metadata against its own hardware settings. A mismatch — such as a file sliced for a 0.4mm nozzle when a 0.6mm nozzle is installed, or a profile for an older firmware version that does not include a feature the current firmware expects — triggers this warning. The printer will typically allow you to continue printing despite the warning, but dimensional accuracy and extrusion amounts may be incorrect if the hardware configuration genuinely differs.

Step-by-Step Fix

1. Open the print file in PrusaSlicer and verify the printer profile. In PrusaSlicer, confirm the printer profile in the top-right dropdown matches your exact model. Check the Print Settings and Filament Settings as well.
2. Verify the nozzle diameter in PrusaSlicer matches your installed nozzle. In PrusaSlicer, go to Printer Settings → Extruder 1 and check the Nozzle diameter field. Match this to the nozzle you have physically installed.
3. Re-slice the file and export a new G-code. After confirming the profile is correct, re-slice the model and save the new G-code to your USB drive or Prusa Connect.
4. On the printer, confirm hardware settings match the installed nozzle. Navigate to LCD Menu → Settings → Hardware and verify the nozzle type and diameter listed on the printer match the nozzle installed in the Nextruder. Update these settings if you have changed nozzles.
5. Update PrusaSlicer to the latest version. Older slicer versions may not embed the metadata format that current firmware expects. Update PrusaSlicer from prusa3d.com/downloads.

Parts Required

• No replacement parts are required for this fix — this is a slicer settings and profile issue

If the warning appears even after re-slicing with the correct profile, contact Prusa Support at help.prusa3d.com with the G-code filename and your hardware settings.

Frequently asked questions

What does Prusa 13803 mean?

Prusa error 13803 (G-Code Not Fully Compatible) appears on the MK4 and its equivalents are #31803 on the CORE One, #26803 on the MK4S, #27803 on the MK3.9S, #28803 on the MK3.5S, #21803 on the MK3.9, #23803 on the MK3.5, #17803 on the XL, and #12803 on the MINI. The print file contains G-code that was sliced for a hardware configuration that does not fully match what the printer has installed — most often a nozzle diameter mismatch.

How do I fix Prusa 13803?

Prusa error 13803 means the print file G-code doesn't match the printer's hardware configuration. Learn how to re-slice with the correct profile to resolve the mismatch.