Siemens Fault 0a7991 Best Jun 2026

If the alarm does not clear after a successful ID run or power cycle, try these steps: Siemens SiePortalhttps://sieportal.siemens.com How can resolve the alarm Code 7991 and 8526 - SiePortal

: Set p1900 = 0 and p1300 = 0 (V/f control mode).

While it's technically an "alarm" rather than a "fault" (meaning it shouldn't always trip the system immediately), it will prevent the drive from entering its normal operation mode until addressed. Here is a comprehensive look at what causes A07991 and the best ways to resolve it. What is A07991?

There are two primary ways to clear this alarm. The first is the standard procedure; the second is for experienced users in specific scenarios. siemens fault 0a7991 best

The code (commonly referred to as A7991 or A07991 in Siemens documentation) is a specific alarm for Siemens SINAMICS drives, such as the G120, G130, or S120 series. It indicates that Motor Data Identification is Activated . Understanding Alarm A7991

The (often seen in SINAMICS G120/G120C drives) indicates that Motor Data Identification is activated . This is not a "fault" that stops the drive, but rather a warning/status alarm that remains until the identification process is completed or manually deactivated. Quick Fixes

One of the primary instigators of this fault is improper parameterization during commissioning. Siemens drives operate on a vast matrix of parameters, many of which are interdependent. A frequent scenario involves the modification of "Function Blocks" (FBs) or technology applications (such as DCC charts) without correctly updating the associated drive objects. If a user modifies a parameter set via STARTER or TIA Portal and downloads it to the drive, but the underlying firmware version or the memory allocation for the logic blocks does not match the project file, the drive may throw Fault 0A7991 upon initialization. Essentially, the drive is "confused" because the software blueprint it received does not align with the hardware reality or the memory capacity of the Control Unit. If the alarm does not clear after a

The application demands more torque than the motor can produce.

Navigate to the commissioning menu in STARTER or Startdrive.

| Aspect | Detail | |--------|--------| | | 0A7991 | | Display text | "CU: Internal communication error" | | Main cause | EMI, firmware mismatch, CU overload | | Best first fix | Check grounding & shielding | | Best software fix | Increase p2040 or p2079 tolerance | | Criticality | High – drive stops immediately | | Typical affected series | SINAMICS G120, S120, G130, SIMOTION | What is A07991

Enable the drive and give a start command. The motor will run, and the alarm should disappear upon success. 2. Complete Configuration and Run Motor ID at Standstill

: Carry out the motor ID at standstill as prompted by the system.