Code 231-A8F0: Drive lock %1 - safety function STO is active
Issue Description & Safety Warning
The Heidenhain TNC Series CNC has triggered a critical Drive lock %1 - safety function STO is active 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] - Drive switch-on was prevented because the safety function STO is presently active for this drive. - The STO safety function could not be exited. Exiting the STO safety function requires the following: The activation of the axis group through the SPLC program (PP_AxGrpActivate of the associated axis group) Enabling of the drive by the SPLC program (PP_AxFeedEnable of the associated axis) The switch-on command of the PLC program (PLC Module 9161) - If the message appears during the current controller adjustment of the spindle, the "spindle start" key was not pressed before the adjustment was started. [Error correction] - Press the "spindle start" key before the spindle adjustment - Press the key for moving the axis on the machine control panel for a longer time - Optimize program processes in the PLC and SPLC program - Check the SPLC program and correct if necessary - Inform your service agency
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 231-A8F0 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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