Siemens Fault 0a7991 Jun 2026

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

The is a common notification that appears on Siemens variable frequency drives (VFDs), most notably within the SINAMICS G120, G120C , and S120 drive series .

Here’s a technical support-style post regarding Siemens fault (often written as 0a7991 or A07991 depending on the drive family). siemens fault 0a7991

This code is not simply a “stop” signal; it is a sophisticated protective response from the drive’s internal monitoring system. If you are seeing 0A7991 on your Siemens SINAMICS G120, S120, G130, or G150 drive, you are dealing with a critical torque/speed deviation or a condition.

The drive has lost power or experienced a hard reboot before a previously scheduled motor identification routine could finish successfully. This alarm frequently appears alongside , which indicates

If the drive now runs, you have a tuning issue – not a hard mechanical failure.

I’ll help narrow it down further.

The alarm A07991 triggers because the drive is waiting for a to execute this diagnostic routine. The root causes typically include: Dealing with Motor ID ( code 7991 ) - SiePortal - Siemens

: If a drive restarts while waiting for a measurement command, the request can get stuck or reset, keeping the alarm flagged on subsequent boot-ups. This code is not simply a “stop” signal;