Siemens Fault 0a7991 [2021] May 2026

: Ensure the Profinet/Profibus cable is securely plugged in and the PLC is powered on.

: While this alarm is active—especially if a rotating measurement is selected—you may be unable to save parameter assignments to the ROM until the process finishes. Common Troubleshooting Steps

Set (Motor data identification and rotation test: Disabled). siemens fault 0a7991

Apply a (start signal) to initiate the routine.

Removes the requirement for motor details for initial testing. : Ensure the Profinet/Profibus cable is securely plugged

This alarm frequently appears alongside , which indicates a communication timeout with a PLC.

When this code appears, the drive is notifying you that a motor identification routine has been scheduled or is currently running. This routine is essential for the inverter to learn the electrical characteristics of the connected motor (such as resistance and inductance) to ensure precise control. Apply a (start signal) to initiate the routine

Set (Control mode: V/f standard) if advanced vector control isn't needed immediately. 3. Resolving Persistent Alarms (A07991 + A8526)

: If testing the drive standalone, set p2030 = 0 (No protocol) and perform a "RAM to ROM" save. Technical Summary Table Default/Action Description p1900 Set to 0 Disables the motor identification routine. p0971 Set to 1

The most direct fix is to allow the drive to perform the check.