Seat Exeo Stiff Steering

That sounds tricky. The symptoms you describe, increased steering effort and vibrations, point to something wrong with your power steering system, possibly influenced by the steering angle sensor. The steering angle sensor is important as it communicates steering wheel position and speed to your car's computer, which then adjusts traction control and stability. A faulty sensor might throw off these systems, leading to alignment problems, which is why you feel vibration. Has the car had any alignment or wheel work done recently?

Thanks for the quick reply. It's interesting what you say about traction control. I haven't had any alignment work done recently, but is there a way to check the steering angle sensor myself, or is it best left to professionals?

Given the symptoms and your car's age, a faulty or miscalibrated steering angle sensor is a strong possibility. These automotive sensors are critical. While there are ways to check some sensor data with the right diagnostic tools, messing with the steering system without proper knowledge can be risky. Honestly, for something like this, taking it to a workshop with experience in automotive sensors and alignment problems is the safest bet. They can properly diagnose the issue and recode the sensor if needed.

Just to let you know, you were right. I went to a workshop, and the steering angle sensor coding was faulty. They recoded it, and the problem is gone. It was 195€. Thanks for the help.