2125

Special Unit Recognition/Response Error

Mitsubishi Electric · MELSEC System Q/L Series

What does 2125 mean?

This error occurs when an intelligent function module or special function module is installed but is either not recognized by the CPU (QCPU/LCPU) or fails to respond. This suggests a compatibility issue, incorrect module type, or a hardware fault within the module itself. The error is diagnosed at power ON or reset and will cause the CPU to stop.

Common Causes

  • An installed module is not recognized as compatible by the QCPU or LCPU.
  • The intelligent function module or special function module is experiencing a hardware fault preventing it from responding.
  • Incorrect module type or version installed for the specific CPU model.

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Verify that only usable and applicable modules compatible with the CPU (QCPU/LCPU) are installed.

  2. 2

    Inspect the physical seating and connections of the intelligent function module or special function module.

  3. 3

    Reset the CPU module and attempt to transition it to RUN mode.

Browse all codes in this manual (53)
Verified technical data. Last updated: March 2026

Related Faults

Source: Mitsubishi Electric MELSEC System Q/L Series