Siemens G120 F01205 — What It Means
F01205 on a Siemens SINAMICS G120 is labeled ‘CU: Time slice overflow.’ It means the control unit did not finish its required processing within the allotted time slice, so the drive trips with an OFF2 reaction. The fault must be acknowledged by a POWER ON cycle. The root cause is insufficient computation time in the control unit for the existing topology or task load it’s handling.
This is a control-unit performance fault, not a motor or power-stage issue. It appears when the CU is overloaded by too many drives on the bus, complex parameterization, heavy communication tasks, or occasionally a firmware or CU hardware problem.
Common Causes
- Too many drives or bus devices on the control unit The CU is handling more topology or communication load than its processing time allows, especially in multi-drive or bus-heavy setups.
- Sampling times set too fast Short sampling intervals increase the computation burden on the control unit and can push it past the available time slice.
- Complex control or parameter configuration Heavy or intricate parameterization increases CPU demand on the CU and can trigger the overflow fault.
- Firmware issue or outdated control-unit software Old or corrupted firmware can cause inefficient processing and lead to persistent time-slice faults after power cycling.
- Faulty or failing control unit hardware If the CU itself has internal defects, it may not complete tasks in time even with a normal load.
Step-by-Step Fix {#fix}
- Record the fault and fault value from the drive diagnostics or fault buffer in Startdrive or TIA Portal before clearing it, since Siemens uses the fault value for internal troubleshooting.
- Perform a full POWER ON cycle of the drive and system, because Siemens lists POWER ON as the required acknowledgement method for F01205.
- Check if the fault returns immediately or only under load or communication conditions to determine whether the issue is tied to active topology or a permanent CU problem.
- Reduce the number of connected drives or devices on the control unit if the fault appears under multi-drive or bus-heavy conditions, following Siemens guidance to lower the topology load.
- Increase sampling times in your drive parameters where the application allows it, as this directly reduces the computation burden on the CU.
- Review recent parameter changes and communication structure in your commissioning software to identify any new configurations that may have increased processing demand.
- Update the firmware or replace the control unit if the fault persists after a clean POWER ON and simplification of the topology, since Siemens-derived remedies include firmware upgrades and CU replacement for unresolved cases.
Parts Often Needed
| Part | Notes |
|---|---|
| Siemens SINAMICS G120 Control Unit (CU) | Amazon | Required if the fault persists after power cycling and topology reduction. Match your CU model and firmware version. |
| G120 firmware update package | Amazon | Download from Siemens support portal. Install via TIA Portal or Startdrive if the CU is healthy but the fault is software-related. |
When to Call a Pro
Call a qualified Siemens technician or your local Siemens service hotline if the fault remains after a POWER ON cycle, topology simplification, and firmware update. Because F01205 involves internal control-unit processing and time-slice management, it may indicate a CU hardware defect or a configuration issue that requires advanced diagnostics in TIA Portal. If you are not experienced with drive commissioning, multi-drive networks, or Siemens parameter structures, get professional help before replacing the control unit or making changes to your communication topology.