Siemens G120 F01625 - Causes & Fix

What this code means

Fault code F01625 on a Siemens SINAMICS G120 drive indicates a sign-of-life error in the safety data. This is a Safety Integrated communication fault where the drive has detected a mismatch, loss of the expected cyclic heartbeat between internal safety processors, or a timing problem in the safety channel. When this fault occurs, the drive initiates a safety reaction and executes a STOP A to protect personnel and equipment.

The drive’s two internal safety processors continuously exchange status messages to verify that safety functions are working correctly. When that communication fails or the timing window is violated, F01625 is logged. Siemens documentation ties this fault to safety communication discrepancies and warns that if the fault cannot be acknowledged after troubleshooting, the Control Unit may require replacement.

Common Causes

• EMC or wiring interference Poor cabinet design, improper cable routing, or electromagnetic interference disrupting the internal safety communication path between processors.
• Incorrect voltage on safety input An inadmissible voltage such as 230 V applied to a safety input circuit instead of the correct low-voltage signal.
• Safety processor communication failure A hardware or firmware fault preventing processor 1 and processor 2 from exchanging safety heartbeat messages.
• Safety software time-slice overflow The internal safety task cycle took longer than allowed, causing the sign-of-life watchdog to trip.
• Unresolved safety discrepancy A prior safety alarm or mismatch that was not properly acknowledged or cleared before normal operation resumed.
• Miswired or open safety circuit Loose connections, broken wires, or incorrect termination in the Safe Torque Off or PROFIsafe wiring harness.

Step-by-Step Fix

1. Read all active faults and alarms in the drive display or via the Starter software to identify whether F01625 appears alone or with additional safety or communication faults that point to the root cause.
2. Check cabinet EMC layout and cable routing against Siemens installation guidelines, separating power and safety signal cables, verifying shielding continuity, and confirming proper grounding of cable shields at both ends.
3. Inspect all safety input wiring for incorrect external voltage, loose connections, or miswiring, and confirm no inadmissible voltage such as 230 V is present on any safety terminal.
4. Perform a safety acknowledgement cycle by toggling the Safe Torque Off input (deselect and reselect STO) according to your safety configuration, then attempt to clear the fault via the control panel or commissioning tool.
5. Power cycle the drive completely by removing all supply power, waiting at least 30 seconds for capacitors to discharge, then restoring power and monitoring whether the fault reappears on startup.
6. Test with minimal wiring by disconnecting any external safety devices or PROFIsafe network connections, leaving only the basic STO circuit, and checking if the fault persists to isolate internal versus external causes.
7. Replace the Control Unit if the fault cannot be acknowledged after all wiring and power cycle steps, as Siemens documentation specifies Control Unit replacement when F01625 remains uncleared.

Parts Often Needed

When to Call a Pro

Call a qualified drives technician or Siemens-certified integrator if you are not trained in functional safety systems or if the fault persists after basic wiring checks and power cycles. Safety Integrated diagnostics often require access to the Safety Integrated commissioning software, knowledge of SIL-rated circuit design, and the ability to interpret internal safety processor logs. If your application is SIL 2 or SIL 3 rated, any troubleshooting or part replacement must be performed and documented by personnel with the appropriate safety certification to maintain compliance with machinery directives and local regulations.