Siemens Sinamics drives are widely used on CNC machine tools — particularly Sinumerik 840D sl and 828D controls — and topology faults are among the most common, and most misdiagnosed, error states. A topology fault means the drive system has detected a mismatch between the expected hardware configuration and what's actually connected. That mismatch could be a failed component, but it's equally likely to be a configuration issue, loose connection, or power sequencing problem.
What the Topology Fault Actually Means
The Sinamics drive stores a "topology" — a map of every drive component in the system. This includes Control Units (CUs), Motor Modules, Line Modules, Sensor Modules (SMCs), and Terminal Modules (TM). When the drive powers up, it compares what it detects on the DRIVE-CLiQ network against this stored topology. Any difference triggers a topology fault.
The fault number will tell you exactly which component is mismatched. The most common topology fault codes are:
- F01650 / A01650: Topology comparison — a component is present but doesn't match the stored configuration
- F01655: Drive object not found — the control expects a component that isn't responding
- A01315: Component changed — a component serial number has changed (often after replacement)
Don't Jump to Hardware Replacements
Before ordering a replacement drive module, check these in order:
DRIVE-CLiQ cables: Reseat every DRIVE-CLiQ connector in the chain. A single poorly-seated RJ45 connector can cause cascading topology faults across multiple drive objects. DRIVE-CLiQ cables carry both communication and 24V power to sensor modules — a bad connection affects everything downstream.
24V power supply: Each Motor Module has its own external 24V supply. If a module's 24V supply is below 20.4V or missing entirely, it won't respond on the DRIVE-CLiQ bus and will appear as a topology fault. Check the green LED on each module — if it's dark, you have a 24V issue, not a drive failure.
Topology comparison in STARTER / Startdrive: Connect your PC to the CU and open the topology screen. The software will highlight exactly which slot has the mismatch. If it's a serial number change and the component type matches, you can often accept the new topology without any parameter changes.
When Topology Changes Are Expected
If you've intentionally replaced a component — say swapping a failed Sensor Module — the new unit will have a different serial number. The control will raise a topology fault on next power-up. Use Startdrive or STARTER to perform a "topology comparison" and accept the new component. The drive will then remap the new serial number into the stored topology.
Spares to Keep on Hand
For shops running Sinamics S120 systems, we recommend keeping a spare Sensor Module (SMC20 or SMC30 depending on your encoder type) and at least one spare DRIVE-CLiQ cable of each length used in your machine. These are the most common failure points and having spares available avoids days of downtime waiting for a replacement.
Browse our Siemens spares category for Sinamics-compatible DRIVE-CLiQ cables, encoder modules, and replacement cooling fans.