Siemens - Fault 0a7991

: A food processing plant using a SINAMICS G120 to drive a dough mixer reports recurring fault 0A7991 every morning at first start, but runs fine rest of the day.

: Ensure the Profinet/Profibus cable is securely plugged in and the PLC is powered on.

By understanding the typical causes—faulty modules, loose connections, configuration mismatches, or wiring shorts—and following the step-by-step diagnostics outlined in this guide, you can minimize downtime. Always remember to check the diagnostic buffer first, verify the hardware online, and keep OB 122 in your program as a safety net. siemens fault 0a7991

If you cannot perform the ID run (e.g., during a Factory Acceptance Test without the final motor), you can inhibit the function .

. Here is how to handle these specific errors if they are what you're seeing: Common Related Siemens Faults A07991 (Drive: Motor data identification active) : A food processing plant using a SINAMICS

Depending on the identified root cause, here are the appropriate solutions.

If you do not wish to perform the identification (e.g., during testing with a dummy load), manually set (Inhibited). In some control modes, you may also need to set (V/f control) to bypass advanced motor modeling. step-by-step instructions Always remember to check the diagnostic buffer first,

Once the root cause is identified, here is how to eliminate 0A7991 permanently.

Ensure the motor is mechanically safe to receive brief voltage pulses. For stationary measurement ( p1900 = 1 ), the motor shaft will generally not rotate, though it may emit a high-pitched whistling noise.

Siemens drives are robust, but they rely on precise communication between their internal and external components. Fault 0A7991 is a signal that this communication chain has been broken. By methodically checking your firmware, cables, and configuration, you can usually isolate the problem quickly.

Open your active commissioning folder and explicitly trigger a RAM-to-ROM copy ( p0971 = 1 ) . If you bypass this save, the alarm will reappear the next time the mains power disconnects.