Code 26204: [Channel %1: ] Block %2: The chain element %3 referred to in $NK_NEXT[%4] is already contained in the chain
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical [Channel %1: ] Block %2: The chain element %3 referred to in $NK_NEXT[%4] is already contained in the chain 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 = Channel number %2 = Block number, label %3 = Name of the next chain link %4 = Index of the chain element Diagnostics Manual (DAsl), 03/2009 Definitions: In one chain link, the next link of the chain is indicated as a chain link already in existence in the chain. This allows you to define a not permitted closed chain. Reaction: Correction block is reorganized. Interface signals are set. Alarm display. Remedy: Define the kinematic chain in such a way that no closed chain results. Program Continuation: Clear alarm with NC ST ART or RESET key and continue the program.
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 26204 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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