Siemens Fault 0a7991 〈2025-2026〉

Understanding Siemens Alarm A07991: Motor Data Identification Activated

If a drive's power supply is cut while a previously requested identification sequence is pending, the drive re-boots with the A07991 alarm pending until it receives a run command to perform the calculation. Understanding the Companion Alarm: A08526

The alarm commonly appears during three distinct lifecycle stages:

The Siemens drive code (more commonly documented in engineering environments as A07991 or A07991 (N) ) signifies "Drive: Motor data identification activated" .

When you encounter F07991 on a Siemens SINAMICS panel or Starter/TIA Portal, follow this structured diagnosis.

Once the internal mapping registers update successfully, parameter p1900 drops back down to 0 , and the A07991 alarm clears automatically.

[Alarm A07991 Activated] │ ├─► Motor is locked from running normal production speeds ├─► System parameters cannot be permanently written (RAM to ROM) └─► Drive awaits a "Run Command" to begin short tuning sequence

Running a basic setup script through software like Startdrive or Starter automatically schedules a motor identification run.

| Step | Action | |------|--------| | 1 | Clear mechanical obstruction. | | 2 | Increase torque limit (temporarily for testing). | | 3 | Check brake control logic & power supply. | | 4 | Perform encoder test (p2500, p2504). | | 5 | Recalculate motor parameters (p304, p305, p311). | | 6 | Disable "stall detection" temporarily (p2178) for diagnosis only. |

To troubleshoot and resolve fault code 0A7991, follow these steps: