Code 126-007F: Self-test cannot be started
Issue Description & Safety Warning
The Heidenhain TNC Series CNC has triggered a critical Self-test cannot be started 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] Before the self-test (emergency stop test), an error occurred that prevents the test from starting: - Emergency stop error has occurred - Emergency stop button was pressed - Emergency-stop circuit is defective - Internal temperature of an HSCI component is too high - Internal temperature of an HSCI component is too low - The fan of an HSCI component is defective - The power supply to the component is missing, too low or too high - HSCI cabling is missing or defective [Error correction] - Note further messages. - Use the HSCI bus diagnostics to find out which components are reporting an error - Check the emergency-stop circuit - Check the power supply to the affected HSCI components - Check the HSCI cabling - If necessary, exchange the HSCI component - Generate the service files and inform your service agency [10] 10/2023
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 126-007F 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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