Code 12495: Channel %1 Block %2 Change (definition) of data class %3 is not allowed here
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical Channel %1 Block %2 Change (definition) of data class %3 is not allowed here 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 = Data class Definitions: Change of the data class in this ACCESS file or defin ition in this GUD file (for file name see alarm 15180) not possible. Priority of the new data class may only be smaller or t he same as that of the definition file. This means that DCS may only be programmed in SGUD (SACCESS), DCM not in UGUD and GUD9 (UACCESS), DCU not in GUD9. DCI is allowed in all GUD and ACCESS files. Reaction: Correction block is reorganized. Interface signals are set. Alarm display. Remedy: Program the data class of the area permi ssible for this GUD or ACCESS file. 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 12495 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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