Code 28001: NCU link connection to the NCU %1 of the link network has been aborted
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical NCU link connection to the NCU %1 of the link network has been aborted 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
Parameters: %1 = NCU number Definitions: All NCUs in the NCU link network exchange data cyclica lly (sign-of-life). If this alarm occurs, sign-oflife signals have not been received from one other NCU on the NCU network. (see alarm parameters) This fault in the link can have various causes: - Defective hardware. - The machine data which configure the NCU link are not identical on all NCUs. - An identical interpolator cycle ti me has not been selected on all NCUs. Reaction: NC not ready. Channel not ready. NC Start disable in this channel. Interface signals are set. Alarm display. NC Stop on alarm. Remedy: - Check the IPO cycle on all the NCUs. - If necessary, check NCU li nk-specific alarms first. Program Continuation: Switch control OFF - ON. Diagnostics Manual (DAsl), 03/2009
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 28001 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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