Hyundai Repair: Speed Sensors, vehicle speed sensor, 2002 hyundai sonata

Question
My check engine light is on.  I put my 2002 Hyundai Sonata on a computer and got two codes. P0500 and P0715.  I went to a auto parts store and was given a speed sensor.  I replaced the speed sensor and now my speedometer works, but I still need to replace the other sensor.  My check engine light is still on.  The problem is I don't know which sensor I replaced.  Can you tell me which sensor I still need to replace? Or which sensor it is that controls the speedometer? Help!  

Answer
Your speedometer is controlled by the vehicle speed sensor on the top of the differential of the transmission.  I presume that's the one you've already replaced.  

P0500 indicates an error in the vehicle speed signal from the sensor read by the Engine Control Module (ECM).  On four cylinder cars, this is the sensor described above for the speedometer.  On V6 vehicles, this signal is provided by the right front wheel speed sensor.

P0715 refers to an error in the signal received by the transmission control module (TCM) from the input speed sensor.  Every time I've seen this code, it's been caused by the input speed sensor itself.  It's located on top of the transmission approximately half under the bracket holding the shift cable.