Siemens Fault 0a7991 Best Hot! Info

(often appearing as ) indicates that Motor Data Identification is currently activated on your Siemens SINAMICS drive

(such as the G120, G120C, or S120). This is a commissioning alarm, not necessarily a hard fault, meaning the drive is waiting to perform a measurement of the motor's electrical characteristics. Siemens SiePortal How to Resolve Alarm A07991

Depending on whether you want to complete the identification or bypass it, use one of the following methods: How can resolve the alarm Code 7991 and 8526 - SiePortal siemens fault 0a7991 best

3. Step-by-Step Troubleshooting Guide

Phase 2: The Identification Sequence (No Fault 0A7991)

  1. Set p0010 = 3 (Motor identification).
  2. Set p1900 = 1 (Enable static identification – no rotation).
  3. Crucial Step: Go to the Parameter View and set p1910 = 1.
  4. Remove the "OFF" command. Ensure there is no active OFF1 or OFF2 signal.
  5. Send an "ON" command (Start the drive via terminal 5, PLC, or panel Run key).
  6. Observe: The motor will hum for 10–60 seconds. No fault 0A7991.
  7. Result: p1910 automatically resets to 0; r1910 shows "Identification OK."

Mastering Siemens Fault 0A7991: The Best Troubleshooting Guide for SINAMICS Drives

Date: October 2023
Product Scope: SINAMICS G120, G120C, G120D, S120 (CU2xx-2 series)
Keyword Focus: siemens fault 0a7991 best

Siemens Fault 0A7991: The Best Diagnostic and Fix Guide

If you’ve landed here, you’ve likely just seen the dreaded 0A7991 alarm flash up on your Siemens drive (Sinamics) or PLC system. Don’t panic. While this fault can stop a production line in its tracks, it is usually straightforward to resolve once you know exactly where to look. (often appearing as ) indicates that Motor Data

In this post, we break down the best practices to diagnose, troubleshoot, and clear Fault 0A7991 for good.

✅ Step 2 – Check grounding & shielding (most effective fix)

1. Understanding the Fault

Siemens drives (SINAMICS G120, S120, Masterdrives) use incremental encoders to track motor speed and position. These encoders send three sets of signals: Track A, Track B, and Track R (Zero/Reference pulse). Set p0010 = 3 (Motor identification)

Fault 0A7991 triggers when: The drive receives A and B signals (indicating the motor is spinning), but it fails to detect the "R" pulse (the zero marker) after one full revolution. The drive essentially "loses its place."

Preventing Future Occurrences: The "Best Practice" Parameters

Once resolved, implement these three best practices to ensure you never see Siemens fault 0A7991 again:

  1. Use a Dedicated Start Command for Tuning: Create a temporary digital input (e.g., DI 3) that sends a positive edge "ON" command only during commissioning. Do not use the production PLC enable.
  2. Lock p1910 after tuning: Set p1910 = 0 (inactive) and set p1900 = 0 (motor identification inactive). This prevents accidental re-triggering.
  3. Document your command source: Add a comment in your PLC code or drive log: "Fault 0A7991 means ‘missing enable.’ Check p0840 before p1910."

1. The Drive is NOT in "Ready" State (Missing Enable)

This is the #1 cause. For safety, Siemens drives require a pulse enable (ON/OFF1 command via terminal or fieldbus) before they perform motor identification. If the drive is inhibited, fault 0A7991 appears.