Prusa error 13602 (USB Not Connected) appears on the MK4 and its equivalents are #21602 on the MK3.9 and #23602 on the MK3.5. The printer attempted to access a USB drive for a firmware update or file print but could not detect a drive in the USB-A port.

What the Error Means

The MK4-family’s USB-A port is the primary local file input for printing without Prusa Connect and for firmware updates via USB. This error fires when the printer’s firmware sends a detection query to the USB controller and receives no response — meaning either no drive is physically inserted, the drive is inserted incorrectly, the drive uses a file system the printer cannot recognize (such as exFAT), or the USB port itself has physical damage preventing electrical contact. A drive that is too large in storage capacity can also cause detection issues on older firmware versions.

Step-by-Step Fix

1. Ensure a USB drive is inserted into the printer’s USB-A port. The port is on the side or front of the printer depending on the model. Confirm the drive is pushed fully into the port.
2. Verify the drive is formatted as FAT32. The printer requires FAT32 format. On Windows, right-click the drive in File Explorer, select Format, and choose FAT32. On macOS, use Disk Utility and select MS-DOS (FAT) format.
3. Use a drive no larger than 32 GB. While some firmware versions support larger drives, 32 GB or smaller FAT32 drives have the most consistent compatibility. Avoid drives over 64 GB.
4. Try a different USB drive. Some drives are not compatible with the USB host controller in the printer. A known-good, standard USB 2.0 flash drive is most reliable.
5. Insert the drive directly without a hub or extension cable. USB hubs and extension cables can affect power delivery and signal integrity. Plug directly into the printer port.
6. Inspect the USB port on the printer for bent pins or debris. Use a flashlight to look inside the USB-A receptacle. Bent pins require professional repair.

Parts Required

• No replacement parts are typically required for this fix — basic tools only
• Replacement USB flash drive (FAT32-formatted, 32 GB or smaller)

If a known-good FAT32 drive is not detected and the port shows no physical damage, contact Prusa Support at help.prusa3d.com for USB host controller diagnosis.

Frequently asked questions

What does Prusa 13602 mean?

Prusa error 13602 (USB Not Connected) appears on the MK4 and its equivalents are #21602 on the MK3.9 and #23602 on the MK3.5. The printer attempted to access a USB drive for a firmware update or file print but could not detect a drive in the USB-A port.

How do I fix Prusa 13602?

Prusa error 13602 means no USB drive was detected. Learn how to check drive format, USB port condition, and correct insertion to restore USB file access.