0a7991: Siemens Fault

Fault Report: Siemens Fault 0A7991

Save Parameters: Once the identification is complete, perform a RAM to ROM copy to ensure the new parameters are saved permanently to the drive's non-volatile memory. Related Faults to Check siemens fault 0a7991

2.5 Encoder or Feedback Failure

• Symptoms: Fault occurs randomly, drive hums or vibrates before tripping.
• Root Cause: A faulty incremental encoder (HTL/TTL) or resolver sends noisy or zero-speed feedback. The drive thinks the motor is stalled because it doesn't see pulses, so it triggers 0A7991.

Subject: Siemens Drive Fault 0A7991 – Cause & Recommended Actions Fault Report: Siemens Fault 0A7991 Save Parameters :

Set parameter p1900 = 0 to de-activate the identification routine . Symptoms : Fault occurs randomly, drive hums or

Fault Code: 0A7991 (A7991)
Associated Products: Siemens SINAMICS drives (G120, S120, G130, G150, etc.)
Fault Class: Alarm / Warning (usually not a trip, but depends on parameterization)

Part 2: Common Symptoms Associated with Fault 0A7991

Before diving into the causes, it is important to recognize how this fault manifests in a live production environment:

Step 2: Identify the Affected Module

The diagnostic buffer usually provides: