Speedometer is not working properly

Hello,

Is this something just happened all of a sudden?
Have you changed the wheel/tire recently?

How did you check the speed for accuracy?

Generally speaking, there is typically 5-7% error in most speedometers. So, it might show 2-3 km over when you are traveling around 40 KPH etc.

Excessive speedometer error can be due to incorrect size wheels/tires or a faulty vehicle speed sensor. An out of calibration sensor can send incorrect signal to the ECM and that will display incorrect speed on the gauge.

I have attached a picture showing the speed sensor location below.

Please let me know if you have any questions.
Thank you.

Hyundai does not allow the speedometer to be reset or calibrated. It is a possibility that the issue could be with the gauge cluster itself as well.
But sensor might be the best place to start.