Siemens Fault 0a7991 Best

This guide provides an in-depth technical breakdown of fault A07991, explaining exactly what it means, why it appears, and the best step-by-step methods to resolve it safely and permanently.

Ensure the motor is at a standstill and the configuration is complete.

The drive receives A and B signals (indicating the motor is spinning), but it fails to detect the "R" pulse (the zero marker) after one full revolution. The drive essentially "loses its place."

tool. It provides a "Help on Fault" button that explains the exact cause and remedy for the specific code active in your hardware. Further Exploration Read about troubleshooting motor overspeed faults on the Siemens Support Forum , which covers F7901 encoder issues. official G120XA solution guide siemens fault 0a7991 best

: Ensure no active safety or communication faults exist on the drive.

: Completing a basic setup where "Motor ID" was selected. Parameter p1960 : Activating speed controller optimization. How to Resolve Alarm A07991

: The drive will apply a stationary current to the motor windings for roughly 10 to 15 seconds. The motor may hum but will not rotate during a standstill test. This guide provides an in-depth technical breakdown of

Check the Profinet/Profibus bus connectors and physical Ethernet cabling.

To minimize the occurrence of Siemens fault 0A7991 and ensure optimal device performance, follow these best practices:

There are two primary ways to clear this alarm. The first is the standard procedure; the second is for experienced users in specific scenarios. The drive essentially "loses its place

If you have a twin drive/motor setup:

This is the #1 cause. For safety, Siemens drives require a (ON/OFF1 command via terminal or fieldbus) before they perform motor identification. If the drive is inhibited, fault 0A7991 appears.