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ErrorLib — Industrial Fault Code Library

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91

Parameter value is not valid in this mode

Danfoss · VLT Micro Drive FC 51

What does 91 mean?

An attempt was made to write an illegal or invalid value to a parameter, or the value is not permissible under the drive's current operating mode. This prevents incorrect settings from being applied that could lead to instability or unsafe operation.

Common Causes

  • Attempting to set a motor control parameter (e.g., speed reference, acceleration time) while the drive is in a specific application mode (e.g., PID mode via Parameter 20-00) that overrides direct parameter access.
  • Attempting to enable a function (e.g., Parameter 2-00, 'Ramp 1 Type') that conflicts with another already enabled or configured function (e.g., Parameter 2-01, 'Ramp 2 Type').
  • Setting a discrete I/O function (e.g., Parameter 5-10, 'Terminal 29 Digital Input') to a value that is only valid for analog inputs.
  • Drive operating mode (e.g., Parameter 1-00) is incompatible with the desired parameter value (e.g., setting a torque limit in V/Hz control mode).
  • Attempting to change a critical operating parameter (e.g., Parameter 1-01, 'Motor Control Principle') while the motor is running.

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Verify the drive's current operating mode (e.g., Parameter 1-00) and ensure it supports the parameter being modified.

  2. 2

    Consult the drive's programming manual for the specific parameter to understand its valid ranges and dependencies on other parameters or modes.

  3. 3

    Stop the motor (output frequency 0 Hz) and ensure the drive is not in an active fault state before attempting to change critical parameters.

  4. 4

    Temporarily disable conflicting functions or switch to a basic control mode (e.g., 'Open Loop V/Hz' in Parameter 1-01) if testing parameter changes.

  5. 5

    Check for interactions with specific application functions (e.g., Parameter 20-00, 'PID Control') that might restrict other parameter modifications.

Browse all codes in this manual (51)
Verified technical data. Last updated: April 2026

Related Faults

00Parameter number does not exist (Register 0007)01No write access to the parameter (Register 0007)02Data value exceeds parameter limits (Register 0007)
Source: Danfoss VLT Micro Drive FC 51
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