Siemens Fault 0a7991 Site

If you cannot run the identification (e.g., during a Factory Acceptance Test without a motor), you can force the alarm to clear by manually changing settings: Set p1900 = 0 (Inhibits Motor ID). Set p1300 = 0 (Switches to V/f standard control mode).

This method allows the drive to perform the calibration, improving motor control and efficiency.

: When the control mode or motor data has been manually reset. Step-by-Step Solutions to Resolve A07991 1. Perform the Motor Identification (Recommended)

“If this is a Factory Acceptance Test (FAT), the correct motor may not be available; make P1900 = 0 to inhibit the 'Motor identification'.” Siemens SiePortal siemens fault 0a7991

By understanding the typical causes—faulty modules, loose connections, configuration mismatches, or wiring shorts—and following the step-by-step diagnostics outlined in this guide, you can minimize downtime. Always remember to check the diagnostic buffer first, verify the hardware online, and keep OB 122 in your program as a safety net.

. This means the drive is waiting to measure the electrical characteristics of the connected motor to optimize its control performance. The Meaning of Alarm A07991

: If you see both, there is likely a communication issue with the PLC. If no PLC is connected, set P2030 = 0 (No protocol) and perform a RAM to ROM save before restarting. If you cannot run the identification (e

Using a newer I/O module (e.g., firmware V5) with an older CPU firmware that does not support it can cause parameter assignment errors.

In some Siemens documentation, is linked to a "Module failure" or "Channel error" on a specific slot of a remote I/O rack (ET 200SP, ET 200M, or ET 200S).

Set p1900 = 2 to perform a standstill identification. This requires the motor to be stopped. : When the control mode or motor data

Issue – Fault A07991 cannot be cleared on SINAMICS G120C drive

Instead of waiting for F07991, configure warning A07991 with a lower threshold:

If the Basic Commissioning wizard in software like STARTER or TIA Portal had Motor ID selected as a step, the drive will output this alarm once the basic setup is complete.

No. It can be a configuration mismatch, network interruption, or even a software issue (missing OB). However, hardware failure is the most common cause after prolonged machine operation.

If you are testing the machine locally without a network connection, set parameter p2030 = 0 (No Protocol) to tell the drive not to look for an active fieldbus line. Perform a RAM-to-ROM save, cycle the 24V control power, and the secondary communication error will drop out.