Siemens: Fault 0a7991

Here’s a technical support-style post regarding Siemens fault 0A7991 (often written as 0a7991 or A07991 depending on the drive family).

• Mechanical check: Shaft rotates freely when cold.
• Parameter check: Motor data correct.
• Live data: On cold start, torque peaks to 180% but speed sticks at 0 RPM for 3 seconds, then fault trips.
• Root cause: The dough hardens overnight. The standard torque limit (p1520 = 150%) and detection time (p2177 = 2s) are insufficient to break the cold dough.

The Siemens A07991 alarm indicates that Motor Data Identification (ID) is currently active or scheduled to run at the next power-on command. This is a standard part of the commissioning process for Siemens SINAMICS drives (such as the G120 or G130) where the inverter measures the connected motor's characteristics to optimize control performance.  Core Cause  siemens fault 0a7991

To resolve this alarm, users on Siemens SiePortal suggest the following: Mechanical check: Shaft rotates freely when cold