Code 4020: Identifier %1 used several times in machine data %2
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical Identifier %1 used several times in machine data %2 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 = String: Name of identifier %2 = String: MD identifier Definitions: When determining a name in the NCK tables (arrays) for: machine axes, Euler angles, direction vectors, normal vectors, interpolation parameters an d intermediate point coor dinates, an identifier has been used that already exists in the control. Reaction: NC not ready. Mode group not ready, also effective for single axes NC Start disable in this channel. Interface signals are set. Alarm display. NC Stop on alarm. Remedy: Please inform the authorized personnel/service departm ent. Select for the identifier to be entered a character string that is not yet us ed in the system (max. 32 characters). Program Continuation: Clear alarm with the RESET key in all channel s of this mode group. Restart part 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 4020 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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