Code 320-0FC4: System overload – message buffer is full
Issue Description & Safety Warning
The Heidenhain TNC Series CNC has triggered a critical System overload – message buffer is full 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
[Cause of error] Very many small jobs were sent in a short time to the PLC run-time system. As a result, the associated messages could no longer be delivered in the system. These jobs result from calling PLC modules or calling the Python function library for OEM applications. The capacity for buffering the messages in the system has been exhausted; the PLC program has been stopped. [Error correction] Change the PLC program or the OEM application Distribute the calls from PLC modules or functions of the JH function library in Python OEM applications more evenly over time. 10/2023 [1125]
Source: HEIDENHAIN NC Error Messages — TNC7/640/620/320/128, CNC PILOT 640, MANUALplus 620 (10/2023)
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Heidenhain TNC Series CNC Alarms
Heidenhain controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code 320-0FC4 on the TNC Series CNC identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Heidenhain's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 4497 Heidenhain TNC Series CNC codes.
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