Why the speed dose not appear

On most cars, this is usually the wheel or trans speed sensor. Run a scan tool across it like this and run the Hyundai eOBD enhanced diagnostics as this may not show as a "common" OBD code. You need something with ABS support, as this may be an ABS code; Not as advanced, but it has the ABS module but beware: IF you need the trans module, it won't work but the 6100p will having the trans module. I have the Blacktec version of the cheaper scan tool I recommended, and I don't like it for stuff like this as I can't see for sure it supports ABS. On one hand, it's my semi-disposable scanner, but I wish I got the 6100p (or the 5610 unless the 6200p was on sale) from the start.

You can see here how to replace it, and get a part number here to see if you can get a better price on the part.