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Siemens SINUMERIK Controller
Safety · Intermediate · 30-120 minutes
Siemens 840D 27255 - PROFIsafe: F module, general error
Alarm 27255 indicates a PROFIsafe F-module communication or functional error detected by the safety protocol layer on the SINUMERIK 840D controller. The alarm fires when the PROFIsafe slave module fails internal diagnostics, loses safe communication, or encounters a safety-critical parameter mismatch that cannot be auto-corrected by the NCK safety runtime.
27255
Siemens 840D 27255 - PROFIsafe: F module, general error
PROFIsafe: F module, general error
Siemens SINUMERIK alarm 27255: PROFIsafe: F module, general error. This alarm indicates a fault or error condition on the SINUMERIK 840D control. Refer to the Siemens SINUMERIK alarm documentation for the complete description and remedy.
Root Cause Summary
Alarm 27255 indicates a PROFIsafe F-module communication or functional error detected by the safety protocol layer on the SINUMERIK 840D controller. The alarm fires when the PROFIsafe slave module fails internal diagnostics, loses safe communication, or encounters a safety-critical parameter mismatch that cannot be auto-corrected by the NCK safety runtime.
Safety
- Refer to Siemens documentation
- Ensure qualified technician performs repairs
Causes and Fixes
- 1
Check PROFINET cable integrity between F-module and NCK. Verify RJ45 connectors are fully seated and not corroded. Use a cable tester to confirm Cat5e/Cat6 compliance.
Do not operate CNC with loose PROFINET connections—safety integrity is compromised.
- 2
Access HMI > Diagnose > PROFIsafe to view module status. Check for 'Communication Error' or 'CRC Fail' flags. Cross-reference the F-module's LED indicators (typically red/amber for error state).
- 3
In NCK menu, navigate to Setup > Safety > PROFIsafe Modules and verify MD 28355 (PROFIsafe timeout in ms) is set appropriate to network load (typical: 100-200ms). If timeout is too aggressive, increase by 50ms increments.
- 4
Perform PROFINET network scan via Siemens TIA Portal or SINUMERIK HMI to confirm F-module IP address is reachable and has no duplicate IP conflicts. Restart the PLC safety task via HMI > System > Warm Restart.
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