Code 6421: [Channel %1: ] Tool move not possibl e. Empty location for tool %2 on magazine %4 not available.
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical [Channel %1: ] Tool move not possibl e. Empty location for tool %2 on magazine %4 not available. 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 ID %2 = String (identifier) %3 = -Not used%4 = Magazine number Definitions: The desired tool motion command - triggered from the MMC or PLC - is not possible. The tool cannot be moved into the specified tool magazine. T here is no appropriate location for this tool. Reaction: NC Start disable in this channel. Interface signals are set. Alarm display. Remedy: - Check whether the magazine data have been defined correctly (e.g. the magazine must not be disabled). - Check whether the tool data are correctly defined (for example, the tool location type must match the location types allowed in the magazine). - Check whether the magazine has simply no more r oom to accept another tool thanks to operating procedures. - Check whether a location type hierarchy is defined and whether, for example, it does not allow insertion of a type 'A' tool in a free location with type 'B'. 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 6421 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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