Siemens Fault 0a7991 Best -

in Siemens drive systems (such as SINAMICS S120 or G120) refers to a

Motor Identification (Motor ID) or Speed Controller Optimization

warning. It is not typically a "fault" that stops the drive, but rather a status alarm indicating that the motor data identification process is active or pending during commissioning. Siemens SiePortal Common Causes Commissioning Phase

: The alarm most often appears when you have triggered a motor identification (p1910) but haven't yet started the motor to let the drive measure its characteristics. Incomplete Configuration

: The drive is waiting for specific motor parameters to be validated or for the "Ram to Rom" copy process to be completed. Siemens SiePortal How to Resolve It Run Motor Identification

: Set the drive to "ready" and give it a start command (with the motor disconnected from the load if performing a rotating measurement). The drive will inject current to measure the motor, and the alarm should clear once the process finishes. Complete the Wizard

: Ensure all mandatory motor parameters (power, voltage, current, speed) are entered correctly according to the motor nameplate. Save Parameters : After the optimization is complete, perform a "Copy RAM to ROM" to ensure the data is saved permanently. Check Fault History siemens fault 0a7991 best

: If the alarm persists or turns into a fault (F-code), use a PC with SINAMICS Startdrive software to check the detailed alarm and fault history for more specific error details. Siemens SiePortal Comparison with Similar Codes Common Solution Motor Identification active Start the drive to complete measurement. Motor Blocked Check for mechanical jams or brake issues. Overcurrent Check for short circuits or ground faults.

For detailed step-by-step instructions, you can refer to the official SiePortal Siemens Support Forum Are you currently using a specific software like Startdrive to configure this Siemens drive? AI responses may include mistakes. Learn more FAULT NO. F30001 - SiePortal - Siemens

(often appearing as ) indicates that Motor Data Identification is currently activated on your Siemens SINAMICS drive

(such as the G120, G120C, or S120). This is a commissioning alarm, not necessarily a hard fault, meaning the drive is waiting to perform a measurement of the motor's electrical characteristics. Siemens SiePortal How to Resolve Alarm A07991

Depending on whether you want to complete the identification or bypass it, use one of the following methods: How can resolve the alarm Code 7991 and 8526 - SiePortal

Fault Definition: Fault code 0A7991 is generally associated with F07900, which signifies a Motor Blocked or Motor Stalled condition in Siemens SINAMICS drives. in Siemens drive systems (such as SINAMICS S120

Description: This error indicates that the drive attempted to move the motor, but the motor did not rotate as expected. The drive detects excessive torque requirement or zero speed when torque is commanded. Causes:

Mechanical Blockage: The load is physically stuck, jammed, or oversized for the motor.

Overload Condition: The application demands more torque than the motor can produce.

Incorrect Wiring/Parameters: Phase loss, incorrect motor wiring, or improper motor data (p03xx parameters) during commissioning.

Faulty Component: Issues with the motor module or motor feedback components. Best Troubleshooting & Resolution Steps

Check Mechanical Load: Ensure the motor shaft rotates freely and there are no jams in the machinery. Perform a power-on reset (disconnect mains for 3

Verify Drive Commissioning: Check the motor data (nominal current, speed, power) in parameters p0300 through p0311 to ensure they match the nameplate.

Check Motor Wiring: Verify that all three phases are connected securely to the motor.

Analyze Torque Limits: Review if the p1520 or p1521 torque limits are set too low.

Motor Inspection: Test for an undersized motor, which may need to be upgraded to handle the load. If you can share: What type of machine this drive is controlling?

Is this a new installation or a machine that was already working? I can give you more specific steps to resolve this. Understanding Siemens Drive Fault Codes | XY Automation

✅ Step 1 – Clear the fault & reset

• Perform a power-on reset (disconnect mains for 3 minutes, then restart).
• If the fault returns immediately or within minutes → proceed below.

Pro Tip: Use Trace Function Before Clearing

Don’t just acknowledge the fault blindly. The best diagnostic move is:

1. Open SINAMICS Startdrive or STARTER.
2. Navigate to Diagnostics > Trace.
3. Record r947 and r949 (fault history buffers). They will often show a sub-code (e.g., 0A7991.0005) that pinpoints the exact offending parameter number.

✅ Step 3 – Review parameter p2040 (PROFIBUS/PROFINET)

• If using fieldbus, check p2040 (monitoring time). Set it slightly higher (e.g., 150 ms instead of 100 ms) to avoid false timeouts.
• For isochronous mode, verify p2079 (synchronization tolerance) is not too tight.

1. The Drive is NOT in "Ready" State (Missing Enable)

This is the #1 cause. For safety, Siemens drives require a pulse enable (ON/OFF1 command via terminal or fieldbus) before they perform motor identification. If the drive is inhibited, fault 0A7991 appears.

• Check: Is the drive showing "O009" (Ready for ON) or "O008" (Switched On/Inhibited)?
• Fix: Switch the drive to "Ready" (p0840 = 1).

Phase 1: Reset and Prep

1. Acknowledge Fault: Press the "FN" + "OK" (BOP-2) or send fault reset via control word.
2. Set Basic Parameters:
   • p0010 = 1 (Commissioning mode)
   • p0304[0] = Rated motor voltage (e.g., 400V)
   • p0305[0] = Rated motor current (Amps)
   • p0307[0] = Rated motor power (kW)
   • p0308[0] = Rated motor power factor (cos φ)
   • p0310[0] = Rated motor frequency (Hz)
   • p0311[0] = Rated motor speed (RPM)
3. Exit Quick Commissioning: Set p3900 = 3 (End quick commissioning with calculation).

✅ Step 4 – Update firmware

• Use SINAMICS Startdrive (TIA Portal) or STARTER software to check for firmware updates.
• Update CU and power unit firmware to the same compatible version.

Preventing Future Occurrences: The "Best Practice" Parameters

Once resolved, implement these three best practices to ensure you never see Siemens fault 0A7991 again:

1. Use a Dedicated Start Command for Tuning: Create a temporary digital input (e.g., DI 3) that sends a positive edge "ON" command only during commissioning. Do not use the production PLC enable.
2. Lock p1910 after tuning: Set p1910 = 0 (inactive) and set p1900 = 0 (motor identification inactive). This prevents accidental re-triggering.
3. Document your command source: Add a comment in your PLC code or drive log: "Fault 0A7991 means ‘missing enable.’ Check p0840 before p1910."

The 3 Best Steps to Fix 0A7991