Code 231-E021: Cut-out signal status incorrect CC%2 Nom:%4 ErrMask:
Issue Description & Safety Warning
The Heidenhain TNC Series CNC has triggered a critical Cut-out signal status incorrect CC%2 Nom:%4 ErrMask: 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
%5 Sgn:%6 [Cause of error] An error occurred in the self-test for safety. A faulty output condition was found before the cut-out channel test: At least on of the examined cut-out signals has the wrong condition. These are the meanings of the abbreviations: Nom (nominal condition of the cut-out signals, decimal notation, interpret in binary): 0: Lock / 1: Release through the corresponding cut-out signal (bits 0 to 9 of Nom) Bit0:STOS.A.MC, Bit1:STO.A.MC.WD, Bit2:STO.A.P.x, Bit3:STO.A.PIC, Bit4:STO.B.CC.WD Bit5:STO.B.P.x, Bit6:STO.A.CC, Bit7:STO.A.SPL.WD, Bit8:STOx.A.RES, Bit9:STO.A.T ErrMask (error mask, decimal notation, interpret in binary): The corresponding switch-off signal (bits 0 – 9 of ErrMask) locks although it should release, or releases although it should lock. Sgn (cut-out signal to be tested): 0: STOS.A.MC 1: STO.A.MC.WD 2: STO.A.P.x 3: STO.A.PIC 4: STO.B.CC.WD 5: STO.B.P.x 6: STO.A.CC 7: STO.A.SPL.WD 8: STOx.A.RES 9: STO.A.T [Error correction] - Check the wiring (PWM cable) - Replace the defective hardware (power module, controller unit) - 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-E021 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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