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
Verify that only usable and applicable modules compatible with the CPU (QCPU/LCPU) are installed.
- 2
Inspect the physical seating and connections of the intelligent function module or special function module.
- 3
Reset the CPU module and attempt to transition it to RUN mode.
Verified technical data. Last updated: March 2026
Related Faults
Source: Mitsubishi Electric MELSEC System Q/L Series