Observed fault pattern
On Sinamics G120 drives using CU240 B-2 and CU240 E-2 control units at firmware 4.6, F01662 "Module Internal communication Error" appeared continuously across roughly 9-10 VFDs, returned every 2-3 hours, and required power OFF/ON to reset. All affected drives were on PROFIBUS and used for pump or agitator duty. Upgrading the control unit firmware from 4.6 to 4.7 reduced how often the fault occurred but did not eliminate it; F01205 "Time Slice Overflow" also appeared intermittently afterward.
| Fault | Evidence meaning | Practical implication |
|---|---|---|
| F01662 | Module internal communication error; cycling power was the only reset reported. | Prioritize the CU-to-module/internal interface path before treating PROFIBUS as the root cause. |
| F01205 | Time slice overflow appeared sometimes after the 4.6 to 4.7 upgrade. | Check control-unit loading and configuration contributors; do not assume firmware alone explains it. |
Isolation procedure
Change one variable at a time and use the previous 2-3 hour recurrence window as the minimum observation period before accepting a result.
- Confirm whether the application uses the CU digital outputs; the evidence repeatedly raises "DO of CU" as a checkpoint, but does not prove it is causal, so record DO usage rather than assuming a fix.
- Swap the power module with an identical/similar VFD in the same machine or project; if F01662 follows the power module, replace or service that module, and if it stays with the CU, continue isolating the control side.
- Swap the communication interface/module between drives and change the PROFIBUS address accordingly; a fault that follows the communication hardware points away from the power module and toward the comms path or address/configuration handling.
- Keep firmware 4.7 during isolation because it measurably reduced recurrence, then escalate remaining F01662/F01205 cases to Siemens support with the fault codes, CU type, firmware versions, topology, and swap results.
Decision logic and constraints
Because all drives were on PROFIBUS yet the reported fault is an internal module communication error, the strongest evidence-backed path is hardware substitution around the CU, power module, and communication module rather than network-only tuning. Treat F01205 as a separate control-unit timing symptom: it may coexist with the same hardware/config stressor, but the evidence does not establish whether DO loading, PROFIBUS traffic, firmware behavior, or a failing module is the trigger. If no conclusion is possible after swaps, collect the exact CU variant, power module rating/model, firmware before/after, PROFIBUS address changes made, whether CU DOs are used, and time-to-fault after each test for vendor diagnosis.
FAQ
What does Sinamics G120 fault F01662 indicate?
The evidence labels F01662 as "Module Internal communication Error" on CU240 B-2/E-2 systems; in this case it recurred every 2-3 hours and needed a power cycle to clear.
Did firmware 4.7 fix F01662 on CU240 drives?
Upgrading from 4.6 to 4.7 reduced fault frequency but did not completely solve the problem, so firmware alone is not sufficient evidence of resolution.
How do I isolate F01662 between the CU and power module?
Swap the power module with a comparable VFD, then swap the communication module and change the PROFIBUS address; whichever hardware the fault follows identifies the suspect path.