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Code 201428: <location>Topo: Comparison connection of a component is different

Issue Description & Safety Warning

The Siemens SINUMERIK 840D CNC has triggered a critical <location>Topo: Comparison connection of a component is 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: Component number: %1, Component class: %2, Connection number1: %3, Connection number2: %4 Drive object: All objects Reaction: NONE Acknowledge: NONE Cause: The topology comparison has detected differences in the actual and target topologies in relation to one component. A component was connected to another connection. The different connections of a component are described in the alarm value: Alarm value (r2124, interpret hexadecimal): ddccbbaa hex: dd = connection number of the target topology cc = connection number of the actual topology bb = component class aa = component number Note: Component class and connection number are described in F01375. The drive system is no longer booted. In this stat e, the drive control (closed-loop) cannot be enabled. Remedy: Adapting the topologies: - change over the actual topology to match the target topology. - download the target topology that matches the actual topology (commissioning software). - automatically remove the topology error (p9904). Note: Under "Topology --> Topology view" the commissi oning software offers improved diagnostics capability (e.g. setpoint/actual value comparison). See also: p9904 (Topology comparis on, acknowledge differences)

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 201428 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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