Code 120402: Bus%1.Slave%2: %3: First commi ssioning of SINAMICS required!
Issue Description & Safety Warning
The Siemens SINUMERIK 840D CNC has triggered a critical Bus%1.Slave%2: %3: First commi ssioning of SINAMICS required! 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 = Bus number %2 = Slave address %3 = Name of the affected drive unit HMI-Alarms Diagnostics Manual (DAsl), 03/2009 Definitions: The drive unit with the bus number and slave address specified in the alarm is in 'First commissioning' state. Reaction: Alarm display. Remedy: Execute first commissioning for the affected drive unit. To do so, switch in the HMI to the dialog 'First commissioning > Drive system > Drive unit, select the affected drive unit, and follow the instructions of the HMI. Program Continuation: Internal
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 120402 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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