391B4550

Error 391 OKI B4550: Troubleshooting and Solutions

The OKI B4550 error 391 indicates a main motor malfunction occurring during initialization or printing cycles. The printer pauses operation to protect mechanical components from further stress. Common root causes include paper debris or sensor misalignments that disrupt rotation speed.

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Common causes

  • 1Internal gear blockage preventing motor rotation.
  • 2Failed sensor pulse in the main drive assembly.
  • 3Worn-out drum unit bushings increasing torque load.
  • 4Electrical surge impacting the motor driver circuit.

Solutions

Diagnóstico rápido

Check if the error 391 appears immediately upon power-up. If the motor makes a grinding noise or fails to rotate the fuser unit, focus your troubleshooting on the physical paper path.

Solución paso a paso

  1. Perform a full power cycle by unplugging the device for one minute.
  2. Inspect the toner and drum area for any loose paper or foreign objects.
  3. Verify that the rollers spin freely when rotated manually in the direction of feeding.
  4. Check the cable connections to the motor assembly if you are technically proficient.

Prevención y mantenimiento

Regularly clean the internal components with compressed air to avoid dust buildup. Using OEM toner cartridges is highly recommended to maintain precise torque on the drum unit. Ensure the environment is free from humidity and dust.

Cuándo llamar a un técnico

If the motor exhibits persistent rattling or the error recurs after clearing all obstructions, the internal controller or the motor itself may require replacement by a certified technician.

Ficha técnica del equipo

  • Technology: Digital LED Monochromatic
  • Speed: Up to 27 ppm
  • Connectivity: USB 2.0, Parallel
  • Capacity: 250-sheet input tray
  • Compatible Consumables: B4500 Series (43502301)
  • Recommended usage: Small office workloads
  • Official drivers / firmware

Steps to follow

  1. 1

    Power cycle

    Turn off the printer, unplug it for 60 seconds, and restart to clear transient controller errors.

  2. 2

    Mechanical check

    Open the access panel and check for any paper debris or obstructions blocking the motor gears.

  3. 3

    Test print

    Run a test page to confirm if the motor rotation issue is resolved.

Frequently asked questions

This error code signifies an issue with the printer's main motor, often related to mechanical resistance or a failed sensor read.

It is considered a system-level error that requires attention; persistent error signals usually indicate a hardware component failure.

The printer uses the B4500 series toner cartridges. Always use genuine parts for better printer longevity.

Cleaning the paper path and rollers every 3 to 6 months helps prevent mechanical failures and sensor errors.