Siemens alarm 21612: Channel %1 axis %2 VDI signal 'Servo enable' reset during motion
SINUMERIK axis alarm (hardware-triggered) · Siemens 840D/810D powerline
What it means
Servo/drive-enable signal dropped while the axis or a geometry-group axis was moving; position loop opened under motion.
Likely causes
- bad connection at terminal T.663 (pulse enable) on 611D control card - most common
- failed internal relay controlled by T.663 on the 611D card
- device-bus (X351) ribbon cable defect
- PLC enable chain drop-out (DBX93.7 / DBX2.1) from e-stop circuit, door interlock or contactor
- drive-side fault collapsing 'Drive Ready' (DBX93.5)
Triage note: Often accompanied by 25201; monitor DBX93.7 during motion to separate PLC-side vs drive-side enable loss.
Replacement parts
We supply the following units for this alarm — tested, warranty-backed:
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6SN1118-…
SIMODRIVE 611D control board (T663 relay) · Primary suspect
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6FX2003-… / X351 ribbon 34-pin
device/equipment bus cable · Common cause
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enable-chain relays/contactors (per machine builder schematic)
PLC enable hardware · Common cause
Need the part urgently?
Send us alarm 21612 with your machine details — typical RFQ turnaround is 24–48h.