400B721dnw

OKI B721dnw 400 Error: Paper Tray Troubleshooting

The OKI B721dnw 400 error is a communication alert associated with the paper input tray. This fault occurs when the machine fails to register the presence of paper or when internal guides are misaligned. It is a manageable error that typically requires a physical check of the paper path.

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Common causes

  • 1Dirty feed rollers preventing paper detection.
  • 2Misaligned sensor tab on the tray.
  • 3Overloaded paper stack preventing tray closure.
  • 4Sensor logic synchronization failure.

Solutions

Diagnóstico rápido

The 400 error on this OKI model presents as a tray recognition failure. If reseating the tray does not resolve the message, the issue likely points to a dirty sensor or misaligned paper guides.

Solución paso a paso

  1. Completely remove the paper tray from the printer unit.
  2. Inspect the feed area for trapped paper fragments.
  3. Verify that the side guides are snug against the paper stack.
  4. Clean the tray sensors using a dry cloth or compressed air.
  5. Reinsert the tray until it locks into position firmly.

Prevención y mantenimiento

Clean the feed rollers every 50,000 pages to prevent dust accumulation. Use high-quality paper to minimize paper dust inside the machine. Original toner cartridges are recommended to keep the internal environment clean.

Cuándo llamar a un técnico

If the tray sensor does not acknowledge the paper after cleaning, the physical sensor component may be damaged or disconnected.

Ficha técnica del equipo

  • Technology: Monochrome laser
  • Performance: 47 ppm
  • Connectivity: USB, Ethernet, Wi-Fi
  • Input capacity: 630 sheets standard
  • Consumables: OKI B721 series toner (Original)
  • Recommended use: Corporate high-volume office
  • Drivers / official firmware

Steps to follow

  1. 1

    Remove tray

    Slide the paper tray out fully and check for obstructions.

  2. 2

    Check guides

    Ensure the side paper guides match the paper size perfectly.

  3. 3

    Cycle power

    Restart the printer to reset the paper feed logic.

Frequently asked questions

Error 400 indicates the printer cannot properly detect the paper tray or the paper stack within it.

It is a non-critical error that halts printing until the sensor is correctly satisfied.

It uses the dedicated OKI B721 series high-yield toner.

Keep the rollers clean and avoid overloading the paper tray.