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ErrorLib — Industrial Fault Code Library

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42EF

Axis is locked for motion commands

Beckhoff · TwinCAT 2 NC

What does 42EF mean?

The axis or group is currently in a locked state, preventing the execution of new motion commands, because a `MC_Stop` command is still actively processing. This safety interlock ensures that an initiated stop sequence completes fully before any new motion is permitted, preventing unintended or hazardous movements.

Common Causes

  • An MC_Stop command is actively processing and its 'Done' output has not yet transitioned to TRUE, indicating the axis has not fully stopped.
  • A follow-up motion command was issued too quickly after an MC_Stop, before the axis reached a true standstill or was released from the stop state.
  • The 'BufferMode' input of the subsequent motion command is set incorrectly, preventing it from aborting or buffering after an active MC_Stop.
  • An internal safety interlock or condition (e.g., software limit) is holding the axis in a locked state following an MC_Stop.
  • Configuration parameter (e.g., P-AXIS-00009, StopDeceleration) is set too low, causing a prolonged stopping sequence.

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    1. Monitor the 'Done' output of the MC_Stop function block; ensure it is TRUE before issuing any new motion commands.

  2. 2

    2. Implement a delay in the PLC logic or check the axis status (e.g., MC_ReadStatus.Stopping is FALSE and Velocity is 0.0) after MC_Stop.

  3. 3

    3. Verify the 'BufferMode' input of subsequent motion commands; ensure it is set to a suitable mode (e.g., ABORTING or BUFFERED) for sequential execution.

  4. 4

    4. Check for any active safety functions or interlocks (e.g., Emergency Stop status, Safety Gate contact) that may be keeping the axis locked.

  5. 5

    5. Review and potentially increase the MC_Stop deceleration rate (e.g., P-AXIS-00009) to reduce the stopping time, if mechanically feasible.

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Verified technical data. Last updated: April 2026

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Source: Beckhoff TwinCAT 2 NC
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