Code 207943: <location>Sync-line-drive: Synchronization not permitted
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical <location>Sync-line-drive: Synchronization not permitted 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
Message value: Parameter: %1 Drive object: VECTOR Reaction: NONE Acknowledge: NONE Cause: Synchronization is not permitted. Alarm value (r2124, interpret decimal): 1300: The control mode (p1300) has not been set to encoderless closed-loop speed control or V/f characteristic. 1910: Motor data identification activated. 1960: Speed controller optimization activated. 1990: Encoder adjustment activated. 3801: Voltage Sensing Module (VSM) not found. 3845: Friction characteri stic record activated. Remedy: Fulfill the conditions for t he line-drive synchronization. Re alarm value = 1300: Set the control mode (p1300) to encoderless closed-l oop speed control (p1300 = 20) or V/f characteristic (p1300 = 0... 19). Re alarm value = 1910: Exit the motor data identification routine (p1910). Re alarm value = 1960: Exist the speed controller opt imization routine (p1960). SINAMICS-Alarms Diagnostics Manual (DAsl), 03/2009 Re alarm value = 1990: Exit the encoder adjustment (p1990). Re alarm value = 3801: Connect-up a Voltage Sensing Module (VSM) and when c onnecting to an adjacent drive object ensure that the drive objects have the same basis clock cycle. Re alarm value = 3845: Exit the friction characteristic record (p3845).
Source: SINUMERIK 840D sl / 840Di sl / SINAMICS S120 Diagnostics Manual (DAsl, 03/2009)
Last reviewed: 2026-07-01 · Verified against the manufacturer’s official documentation.
About Siemens SINUMERIK 840D CNC Alarms
Siemens controllers include extensive self-diagnostics that flag or halt the machine when a fault is detected. Error code 207943 on the SINUMERIK 840D CNC identifies one specific fault condition — its documented cause and the official corrective steps are listed above, sourced from Siemens's service documentation. Always confirm against the manual for your exact machine configuration and follow LOTO procedures before servicing.
Complete Alarm List: 4014 Siemens SINUMERIK 840D CNC codes.
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