Hyundai Repair: 2001anta fe autotransmission down shifting, shade tree mechanic, autotransmission

Question
2001 Santa Fe 2.4 i-4 engine will be driving fine and will all of sudden down shift a gear on its own and the check engine light comes on. Is this a speed sensor problem and it expensive to have fixed? Or can I doit my self I'm a fairly good shade tree mechanic.  

Answer
In most cases, the symptom you describe is caused by either the input or output speed sensor.  To find out, you should have the engine and transmission diagnostic trouble codes read so you know the nature of the problem.  

I suppose "expensive" is in the eye of the beholder, but I certainly wouldn't categorize a speed sensor as a major expense as far as auto repairs go.  If that's the issue, your description of yourself leads me to believe that you'd have no problem with the repairs.