If the drive now runs, you have a tuning issue – not a hard mechanical failure.
Siemens fault 0A7991 is not a mysterious error to dread—it is a precise diagnostic tool. By understanding that it signals either a mechanical obstruction, a fluid dynamics issue (vapor lock), or a parameter mismatch, you can move from reactive fault-resetting to proactive engineering.
The motor commissioning was not completed properly, or the parameter set was not saved after the identification process (RAM to ROM).
A: No. The drive will not execute normal motor operation until the identification sequence has been completed or the alarm has been explicitly deactivated by setting the appropriate parameters to zero.
If you are staging components inside a panel shop or lab environment without a physical motor load connected to the power modules, the drive will lock up or fault out if it tries to pass a diagnostic current. siemens fault 0a7991
A: If motor data identification was selected (e.g., by setting P1910 = 1) before powering down, that selection is lost when the drive is turned off and on again. It must be manually reselected after startup.
If the issue persists after mechanical and parameter checks, provide:
The Siemens fault code is a standard feature of the SINAMICS drive family. It confirms that the drive is ready to measure the connected motor’s parameters in order to optimize performance and ensure safe operation.
: Check p1910 and ensure it is set to 0 to halt active standstill measurements. 3. Perform a RAM-to-ROM Copy If the drive now runs, you have a
This alarm frequently appears alongside , which indicates a communication timeout with a PLC.
No. It occurs on S7-300, S7-400, S7-1200, and S7-1500 systems, but the exact diagnostic text may differ. On S7-1500, it is often accompanied by a more descriptive text like "Module reports channel error."
A: Do not keep resetting. Check for a short on the motor cable (phase-to-phase or ground). Use a megohmmeter.
: In some cases, changing the control mode to basic V/f control can also bypass the need for precise motor identification. 3. Resolving Persistent Alarms (The A8526 Connection) The motor commissioning was not completed properly, or
Because it prevents standard operation until the drive successfully profiles the motor or the function is disabled, engineers and technicians must address it during commissioning or system restarts. Root Causes of Alarm A07991
If you have persistent issues even after following this guide, contact Siemens Technical Support with your diagnostic buffer export and hardware configuration file for advanced analysis.
Create a watch table for the affected input/output addresses. If the values are fluctuating or showing "???" (invalid), it confirms an access issue.
This article covers why this alarm occurs and how to resolve it across various Siemens platforms like the SINAMICS G120, G130, and S120. What is Siemens Fault A07991?