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4465

Position initialization error at system start

Beckhoff · TwinCAT 2 NC

What does 4465 mean?

During the initial system start-up, the set position could not be successfully initialized for all trials (with/without overflow/underflow) within the final position minimum and maximum limits. This means the axis could not establish a valid initial position, preventing it from becoming referenced and ready for motion.

Common Causes

  • Faulty or inconsistent signal from the homing switch (e.g., X4-1, Home Sensor Input), preventing accurate determination of the reference position.
  • Incorrect homing offset parameter (e.g., P4-05, Homing Offset) causing the final position to be outside the allowed min/max range after initialization.
  • Encoder feedback issue (e.g., intermittent signal, noise, or partial damage) resulting in inaccurate position readings during initialization.
  • Absolute position limits (e.g., P3-04 Min, P3-05 Max) are set too tightly, not allowing for the expected range of travel during initialization.
  • Inaccurate or drifting motor/load mechanical coupling, causing the actual position to be different from what the homing procedure expects.

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    1. Verify the functionality of the homing switch (e.g., by manually activating it) and check its input status via diagnostic D-07.

  2. 2

    2. Review and adjust the homing offset parameter (P4-05) to ensure the axis initializes within the absolute position limits (P3-04, P3-05).

  3. 3

    3. Check the encoder signal quality (e.g., A/B phase signals on X3-1, X3-2) with an oscilloscope for noise or dropouts during axis movement.

  4. 4

    4. Expand the configured absolute position limits (P3-04, P3-05) slightly to provide more tolerance during the initial position setting.

  5. 5

    5. Inspect the mechanical coupling between the motor and the load for any play or slippage that could affect homing repeatability.

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Verified technical data. Last updated: April 2026

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Source: Beckhoff TwinCAT 2 NC
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