Code 21700: [Channel %1: ] Block %3 axis %2 touch probe already deflected, edge polarity not possible
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical [Channel %1: ] Block %3 axis %2 touch probe already deflected, edge polarity not possible 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 = Axis name, spindle number %3 = Block number Definitions: The probe programmed under the keyword MEAS or MEAW is already deflected and has switched. For a further measuring operation, the probe signal must first be canceled ( quiescent state of the probe). The axis display is of no signifi cance at the present time but an axis-specific evaluation has been planned for later stages of development. Reaction: Local alarm reaction. NC Start disable in this channel. Interface signals are set. Alarm display. NC Stop on alarm. Remedy: Verify the starting position of the measuring operat ion or check the probe signals in the PLC interface DB10 DBX107.0 / 107.1 (Probe actuated key 1/key 2). Are the cables and connectors in good order? Diagnostics Manual (DAsl), 03/2009 Program Continuation: Clear alarm with the RESET key. 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 21700 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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