Siemens Fault - 0.a7991

This alarm appears when the drive is waiting to perform a routine measurement of the motor's electrical characteristics (identification). It typically occurs: During initial commissioning when a motor ID routine is first selected. After a power cycle

In (without encoder), the drive uses a motor model to estimate speed. If the estimated speed falls below a threshold (default: 1% of rated speed) while the torque limit is active and speed setpoint is > threshold, the drive assumes blockage. siemens fault 0.a7991

The motor data identification routine has been selected (often via parameter P1900 or P1910 ) and is waiting for the next "ON" command to begin. This alarm appears when the drive is waiting

Always follow Siemens safety guidelines. De-energize drive before mechanical inspection. Lock out/tag out. Refer to SINAMICS G120 List Manual (LH1) for firmware-specific details. If the estimated speed falls below a threshold

Remember: This alarm is a protective mechanism. It prevents the NC from sending or receiving garbled data that could lead to unpredictable axis movement or even a crash. Treat the fault with respect, follow the diagnostic steps rigorously, and you will have your machine back in production with minimal downtime.