Ensure all motor data (P0300-P0311) matches the nameplate exactly.
In both cases, the alarm is a good sign—it means you're on the right track to correctly configuring your system.
A hidden gem: 0A7991 frequently appears after a firmware update or when using an older Starter/TIA Portal version. siemens fault 0a7991 best
: Verify parameter p1900 is set to 2 (Identify motor data at standstill) via your keypad (BOP-2/IOP-2) or engineering software.
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: If you don't need the identification (e.g., during testing or a Factory Acceptance Test), set p1900 = 0 to inhibit the process.
If an engineer performs a successful motor identification but neglects to save the drive parameters from volatile memory (RAM) to non-volatile storage (ROM), the drive resets to its unconfigured state after a power cycle. The VFD will request the motor ID again upon reboot. 3. Power Supply Interruptions : Verify parameter p1900 is set to 2
This is generally not the best practice. Disabling motor identification without ever running it can lead to poor motor control, reduced efficiency, higher current draw, and in some cases, overcurrent faults. This method should only be used as a temporary workaround or if you are absolutely certain the drive parameters are already optimized.
Alarm A07991 functions as an operational status flag. In the Siemens diagnostic naming convention, "A" stands for , meaning the drive will continue to run or stay ready, while "F" indicates a Fault that trips the unit instantly.
If you see both:
or "Timeout for internal data exchange"