Code 6410: [TO unit %1: ] Tool %2 has reached its prewarning limit with D = %4
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical [TO unit %1: ] Tool %2 has reached its prewarning limit with D = %4 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 = TO unit %2 = Tool identifier (name) %3 = -Not used%4 = D number Definitions: Tool monitoring: This message informs that the spec ified D offset has reached its prewarning limit for a time-, quantity- or wear-monitored tool. If possible, the D number is displayed; if not, value 0 is assigned to the 4th parameter. If the function additive offset is being used, additive offset monitoring may be active instead of tool wear monitoring. The actual type of tool monitori ng is a tool property (see $TC_TP9). If replacement tools are not being used, the duplo number specifi ed has no meaning. The alarm is triggered through the HMI or PLC (=OPI interface). The channel cont ext is not defined. The TO unit was specified for this reason (see MD28085 $MC_MM_LINK_TOA_UNIT). Reaction: Interface signals are set. Alarm display. Remedy: For information only. The user must decide what to do. Program Continuation: Clear alarm with the Delete key or NC START.
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 6410 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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