Hyundai Repair: SPEED SENSOR, vehicle speed sensor, sonata 4

Question
I have a 2000 Hyundai Sonata 4 cylinder and when i was at a light my check engine lamp came on.  I took my car to the auto parts store and they told me my speed sensor was bad. Where is the speed sensor and how hard is it to replace? thanks

Answer
Your car has three speed sensors.  Unfortunately, none of them would typically cause the check engine lamp to come on when you're stopped.  If you can get me some additional information, I may be able to identify the sensor or narrow it down.  There's a vehicle speed sensor, an input speed sensor, and an output speed sensor.

Can you tell me what the code number was or which speed sensor they're talking about?  Does your speedometer work?  Does your transmission shift abnormally?  Is anything behaving abnormally other than the check engine lamp?