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Code 201355: <location>Topology: Actual topology changed

Issue Description & Safety Warning

The Siemens SINUMERIK 840D CNC has triggered a critical <location>Topology: Actual topology changed 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: %1 Drive object: All objects Reaction: NONE Acknowledge: IMMEDIATELY Cause: The device target topology (p0099) does not corres pond to the device actual topology (r0098). The fault only occurs if the topology was commiss ioned using the automatic internal device mechanism and not using the commissioning software. Fault value (r0949, interpret decimal): Only for internal Siemens troubleshooting. See also: r0098 (Actual device t opology), p0099 (Device target topology) Remedy: One of the following counter-meas ures can be selected if no faults have occurred in the topology detection itself: If commissioning was still not completed: - carry out a self-commissioning routine (starting from p0009 = 1). General: Set p0099 to r0098, set p0009 to 0; for existi ng Motor Modules, this results in servo drives being automatically generated (p0107). Generating servo drives: Set p0097 to 1, set p0009 to 0. Generating vector drives: Set p0097 to 2, set p0009 to 0. Generating vector drives with paralle l circuit: Set p0097 to 12, set p0009 to 0. In order to set configurations in p0108, before setti ng p0009 to 0, it is possible to first set p0009 to 2 and modify p0108. The index corre sponds to the drive object (p0107). If commissioning was already completed: - re-establish the original connections a nd re-connect power to the Control Unit. - restore the factory setting for the complete equipm ent (all of the drives) and allow automatic selfcommissioning again. - change the device parameterization to match the connections (this is only possible using the commissioning software). Notice: Topology changes that result in this fault bei ng generated cannot be accepted by the automatic function in the device, but must be transferred us ing the commissioning software and parameter download. The automatic function in the device only allo ws constant topology to be used. Otherwise, when the topology is changed, all of the previous parame ter settings are lost and replaced by the factory setting. See also: r0098 (Actual device topology)

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 201355 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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