Siemens Fault 0a7991

Diagnosing 0A7991 requires a systematic elimination of possibilities. Here are the five most common physical and parametric causes.

Insufficient power to a remote I/O station (e.g., ET 200M) can cause modules to power cycle, leading to startup errors that manifest as 0A7991.

Conclusion

Troubleshooting Siemens fault code 0A7991 requires a systematic approach, from understanding the fault and its possible causes to performing detailed checks and applying fixes. By following these steps, technicians and engineers can efficiently resolve the issue, minimizing downtime and ensuring the reliable operation of Siemens equipment.

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

The drive is waiting to perform a measurement routine. While this alarm is active, the drive typically cannot be started for normal operation until the identification is either completed or intentionally disabled.  Primary Solutions 

To clear the A07991 alarm, use one of the following methods:  Complete the Identification Routine Give the drive a "Run" or "Start" command.

The motor may "whistle" or make noise for a few seconds during stationary measurement without rotating.

Once the measurement is successful, the alarm clears automatically, and the drive transitions to a ready state. This is a standard part of the commissioning

Disable the Identification ManuallyIf you do not wish to run the identification (e.g., during bench testing or Factory Acceptance Tests (FAT)), change these parameters:

P1900 = 0: Set this to "Inhibited" to disable the motor data identification and rotation test.

P1300 = 0: If the fault persists, some users recommend setting the control mode to "V/f standard".

P0340 = 0: Set this to 0 to remove the requirement for motor details entirely during initial testing. Finalize Configuration (RAM to ROM) If no PLC is connected

After identification is complete or parameters are changed, save the settings by performing a RAM to ROM copy (set P0971 = 1). This ensures the alarm does not return after a power cycle.  Common Troubleshooting Scenarios 

A07991 & A08526 Together: If you see both, there is likely a communication issue with the PLC. If no PLC is connected, set P2030 = 0 (No protocol) and perform a RAM to ROM save before restarting.

Persistent Alarm After Power Cycle: If the alarm returns even after you thought it was finished, it likely wasn't saved to permanent memory. Ensure you perform the RAM to ROM save procedure.  How can resolve the alarm Code 7991 and 8526 - SiePortal