Code 8021: Option 'activation of more than %1 mode groups' not set
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical Option 'activation of more than %1 mode groups' not set 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 = Number of mode groups Definitions: The option for the number of mode groups is not compatible with the activated mode group. Reaction: NC Start disable in this channel. Interface signals are set. Alarm display. Remedy: Add option for more mode groups. Activate fewer mode groups. Program Continuation: Switch control OFF - ON.
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 8021 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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