Code 231-C4A0: Inverter %1 is not active
Issue Description & Safety Warning
The Heidenhain TNC Series CNC has triggered a critical Inverter %1 is not 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] - Charging contactor and main contactor on the supply unit is not on (e.g. connector X70 on UV) - Safety relay not on (e.g. connectors X71 and X72 of the UV, X73 of the HEIDENHAIN expansion board for Simodrive) - PWM bus cable interrupted - Interruption in the electrical cabinet (unit bus, PWM ribbon cable) - Defective inverter, (supply unit and/or power modules, compact inverter) - Inverter switched off (PLC, SH1) - Inverter defective - Motor defective - Humidity has entered the motor - Incorrect motor selected in motor table - Motor power cables mismatched - Motor connected incorrectly [Error correction] - Inform your service agency - Check the inverter and wiring - Check the motor and wiring
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-C4A0 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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