Code 201612: <location>SI CU: STO inputs for power units connected in parallel different
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical <location>SI CU: STO inputs for power units connected in parallel different 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
Message value: Fault cause: %1 bin Drive object: SERVO, VECTOR Reaction: NONE (OFF1, OFF2, OFF3) Acknowledge: IMMEDIATELY (POWER ON) Cause: The drive-based "Safety Integrated" function on the Cont rol Unit (CU) has identif ied different states of the AND'ed STO inputs for power units connected in parallel and has initiated a STOP F. As a result of this fault, after the parameteriz ed transition has expired (p9658), fault F01600 (SI CU: STOP A initiated) is output. Fault value (r0949, interpret binary): Binary image of the digital inputs of the Control Unit that are used as signal source for the function "Safe Torque Off". Remedy: - check the tolerance time SGE changeover and if required, increase the value (p9650). - check the wiring of the safety-relevant inputs (SGE) (contact problems). Note: CU: Control Unit SGE: Safety-relevant input SI: Safety Integrated STO: Safe Torque Off / SH: Safe standstill
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 201612 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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