Code U01---: No user PLC
Issue Description & Safety Warning
The Mitsubishi M800/M80 CNC has triggered a critical No user PLC alarm. Immediate attention from a qualified operator or maintenance technician is required to prevent secondary damage to the equipment or spoiled parts during the manufacturing cycle. Always ensure standard safety and LOTO procedures are followed before accessing electrical cabinets.
Official Troubleshooting Steps
Details No sequence program is included in the built-in ROM or temporary memory area. (1) Sequence program is not stored in the built-in ROM. (2) Sequence program is not written from the GX Developer/GX Works2 or internal PLC edit function. (3) Sequence program cannot be read due to broken built-in ROM. (4) No large capacity PLC additional specifications. Remedy (1) Write the sequence program from the GX Developer/GX Works2 or internal PLC edit function, and then ex- ecute the built-in ROM writing. (2) Check the presence of additional specification "Large PLC capacity" and reconsider the storable size. (3) If (1) or (2) does not solve the problem, there is a possibili ty that built-in ROM is broken.
Source: Mitsubishi M800/M80/E80 Series Alarm/Parameter Manual (IB-1501279)
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Mitsubishi M800/M80 CNC Alarms
Mitsubishi controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code U01--- on the M800/M80 CNC identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Mitsubishi's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 722 Mitsubishi M800/M80 CNC codes.
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