Cause: Autotuning Error comes when a failure in the automatic process of optimizing control parameters for a system. This error can occur due to various reasons, including:

1. Special motor or motor whose power is not suitable for the drive.
2. Motor not connected to the drive.
3. Motor not stopped.

"tnF" fault in Schneider ATV950 drive indicate "Autotuning error". This means the drive encountered a problem while attempting to automatically tune the motor parameters. This process is crucial for optimizing the drive's control of the motor, ensuring efficient and stable operation. 

Here’s a structured approach to troubleshoot and resolve this issue:

1. Initial Checks:

• Restart the Drive: Power off the drive, wait for a few minutes, and then power it back on to reset any transient errors.
• Review Fault Logs: Check the drive’s fault logs for additional details about the autotuning error. This can provide more context and specific fault codes.

2. Verify Motor and Drive Compatibility:

• Motor Type: Ensure that the motor is compatible with the drive and that it is within the drive’s power and current ratings.
• Drive Configuration: Verify that the drive is correctly configured for the type of motor being used (e.g., induction motor, synchronous motor).

3. Check Mechanical Setup:

• No Load Condition: Ensure that the motor is not connected to any load during the autotuning process. Any mechanical load can interfere with the tuning.
• Motor Connection: Verify that the motor is correctly wired to the drive, with secure and proper connections.

4. Parameter Settings:

• Motor Parameters: Confirm that the motor parameters (e.g., rated voltage, current, power, frequency) entered into the drive are accurate and match the motor’s nameplate data.
• Autotuning Mode: Ensure that the correct autotuning mode is selected. Some drives offer multiple tuning modes, such as static tuning (motor stationary) or dynamic tuning (motor running).