Code 402-0009: FK programming: Illegal positioning block
Issue Description & Safety Warning
The Heidenhain TNC Series CNC has triggered a critical FK programming: Illegal positioning block 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] Within an unresolved FK sequence you programmed an illegal positioning block other than FK blocks, RND/CHF, APPR/DEP, and L blocks with motion components exclusively perpendicular to the FK plane. [Error correction] First resolve the FK sequence completely or delete illegal positioning blocks. Geometry functions that are defined over the gray contouring keys and have coordinates in the working plane are illegal (exception: RND, CHF, APPR/DEP).
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 402-0009 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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