Try one or more of the following:
Note: If the message appears after reinstalling the supply, then replace the imaging unit. The imaging unit may be defective or a non‑genuine Lexmark supply. For more information, see Using genuine Lexmark parts and supplies.
31.6x Error Code Reinstall Missing or Unresponsive Imaging Unit (IU)
31.4x error code: Reinstall missing or unresponsive cartridge