Siemens Fault 0a7991 Best [repack] 〈Must See〉
Think of it as the drive saying: “You told me to set this value, but it doesn’t make sense with my current hardware or other settings.”
Engineers testing control panels in a workshop before shipping them to a plant site often encounter this alarm because no physical motor is wired to the VFD terminals yet. The Common Companion: Alarm A08526
A07991 rarely appears in total isolation. Technicians frequently encounter it alongside secondary industrial communication or state faults:
Parameter P1900 (Motor Data Identification) is set to a value that demands identification on the next run, but the run hasn't occurred. Best Methods to Resolve Siemens 0A7991 siemens fault 0a7991 best
If you have access to or TIA Portal diagnostics buffer , check the fault time stamp and see if 0A7991 appears together with other faults (like 0A7992 or 0A7993). That helps narrow down whether it’s a noise or a hardware issue.
If the code is different, it might relate to these common issues found in the Siemens Drive Support Forum Motor data identification has not been performed. Motor locked or speed limit reached. Motor overspeed, often caused by a faulty encoder.
This is the #1 cause. For safety, Siemens drives require a (ON/OFF1 command via terminal or fieldbus) before they perform motor identification. If the drive is inhibited, fault 0A7991 appears. Think of it as the drive saying: “You
The steel mill didn’t care about the blizzard outside, but
: For complex systems, especially industrial ones, it might be necessary to call in a professional technician who is authorized by Siemens or experienced with their equipment.
If you have entered the data manually and do not wish to run the identification (not recommended, but possible for testing): Set parameter P1900 = 0. Step B: Perform a power cycle of the drive (24V and 400V). Step-by-Step Troubleshooting Checklist Expected Result 1 Check P0300-P0311 (Motor Data) Data matches the motor nameplate. 2 Check P1900 Set to 0 if not intending to run ID. 3 Initiate Motor ID (P1900=1) Motor runs, A7991 disappears. 4 Save Configuration Perform RAM-to-ROM to prevent recurrence. Why Proper Motor Data Identification Matters Best Methods to Resolve Siemens 0A7991 If you
performed the most crucial step: . He committed the settings to the drive's permanent memory, ensuring that if the power flickered in the storm, the ghost of A7991 wouldn't return to haunt him.
Set P1900 to an appropriate value (e.g., 1 for identification at standstill, or 2 for identification with rotation).
Furthermore, this fault can arise from volatile memory corruption or failed firmware updates. In industrial environments subject to electrical noise or unstable power supplies, the non-volatile memory (NVRAM) where parameters are stored can become corrupted. If the drive attempts to read a corrupted sector during boot-up or during a specific technological function call, it interprets the garbage data as an invalid value, triggering the fault. Similarly, if a firmware update is interrupted or if an attempt is made to load a parameter set from a newer firmware version onto an older drive unit, the parameter ID mapping will be misaligned, leading to this system-level error.
If the drive is in operation and you try to change parameters (p1910) while it has a speed setpoint, you will see 0A7991.
This is the primary, intended way to handle A07991. Completing the motor data identification (ID) routine is the best practice for ensuring optimal drive performance.
