If you still see the fault, perform a using p0970 = 1 (factory reset) and repeat Phase 1. Corrupted non-volatile memory (NVRAM) is a silent cause of this fault.
A food packaging plant reported daily fault 0A7991 during morning startups on a G120C drive.
| 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 |
in Siemens drive systems (such as SINAMICS S120 or G120) refers to a siemens fault 0a7991 best
The drive has the "ID" command but is missing the "ON" command or hardware enables (like STO) to actually pulse the motor.
The fault code breaks down as follows:
The recommended practice is to allow the drive to perform the motor identification. This ensures the drive is perfectly calibrated to your specific motor, maximizing efficiency and torque control. This is particularly important for applications requiring high precision, such as conveyors in the automotive industry. If you still see the fault, perform a
The drive is operating in standalone I/O control mode, but bus parameters are active.
The Siemens drive triggers this status code when the internal parameter (Motor data identification and rotating measurement) is set to an active state (typically 1 or 2 ). This occurs under three common industrial scenarios:
In Siemens SINAMICS drive systems, the alarm (often referred to as fault 0a7991) indicates that Motor Data Identification is activated . This is not a critical hardware failure but rather a status message indicating the drive is prepared to perform a measurement of the motor’s electrical characteristics. Understanding Alarm A07991 | Aspect | Detail | |--------|--------| | |
Issues with the motor module or motor feedback components. Best Troubleshooting & Resolution Steps
signifies that within the inverter firmware. This state is not an equipment failure, but a required diagnostic routine designed to analyze the electrical characteristics of a connected motor.
: If the drive is stuck and the alarm won't clear, try a factory reset and re-enter basic motor settings before attempting the "Run" command again.
: Give the drive a standard run command via your PLC or control panel. The drive will pass low-frequency currents through the motor windings for approximately 10 to 20 seconds without spinning the shaft.