Hyundai Repair: auto transmission not shifting correctly, advance auto parts, output speed

Question
I have a 2000 sonata, automatic with the four cylinder engine. Recently the transmission will occationally (sometimes I have no problem with auto shifts) lock into third gear while going down the road. I have a check engine light on. the engine runs perfect. I had the code checked at advance auto parts and it said 0720 output sensor malfunction. where is the output sensor located and will changing this sensor fix the shifting problem.

Answer
Chances are very good that replacing the output speed sensor will repair this problem.  It's located on the back of the top of the transmission with a connector with three wires coming out of it.  It'll be partially obscured by the air cleaner box and the wire harness running over top of it.