Prusa error 13321 (Power Panic) appears on the MK4 and its equivalents are #26321 on the MK4S, #21321 on the MK3.9, and #23321 on the MK3.5. The printer detected that the power panic cable — the cable that allows it to detect and survive a power interruption — is missing, disconnected, or damaged.

What the Error Means

Power Panic is a Prusa feature that detects a sudden power loss mid-print, parks the nozzle, saves the print state, and resumes from where it stopped when power returns. This requires a dedicated cable that runs from the PSU to the xBuddy board, carrying a signal that reflects the PSU output voltage. When the printer cannot see this signal, it reports the Power Panic error and disables the feature. Printing can continue without the feature, but any power loss will result in a failed print rather than a recoverable pause. The most common cause is the cable being accidentally disconnected during maintenance or not being reconnected after a printer move.

Step-by-Step Fix

1. Power off the printer and unplug it from the wall. The power panic cable connects near the PSU — never work on PSU connections with power applied.
2. Locate the power panic cable. The cable runs from the PSU (power supply unit) to the xBuddy board. It is typically a single black wire or a two-wire black/white cable depending on the printer variant.
3. Reseat the cable connectors on both ends. Unplug the cable from the PSU tap connector and from the xBuddy board, then reconnect both ends firmly. A connector that is almost-but-not-quite seated can cause this error.
4. Inspect the cable for visible damage. Look for cuts, fraying, or crushed sections along the cable length, especially if it runs through a cable clip or near a moving component.
5. Replace the cable if damaged. Both the single-wire (black) and two-wire (black/white) variants are interchangeable for this function. Use a genuine Prusa replacement to ensure the correct connector type.
6. Power on and verify. After reconnecting, power on the printer and confirm the error no longer appears on the startup screen.

Parts Required

• Replacement power panic cable (if cable is cut or damaged)

If the cable appears undamaged and properly connected but the error persists, contact Prusa Support at help.prusa3d.com — the xBuddy board’s power panic input circuit may need evaluation.

Frequently asked questions

What does Prusa 13321 mean?

Prusa error 13321 (Power Panic) appears on the MK4 and its equivalents are #26321 on the MK4S, #21321 on the MK3.9, and #23321 on the MK3.5. The printer detected that the power panic cable — the cable that allows it to detect and survive a power interruption — is missing, disconnected, or damaged.

How do I fix Prusa 13321?

Prusa error 13321 means the power panic cable is missing or damaged. Learn how to locate, reseat, and replace the power panic cable to restore print-recovery functionality.