Hyundai Repair: Hyundai Sonata Wont Shift on its own, throttle position sensor, transmission control module

Question
I gave my 2002 Sonata 6cyl to my son. The shifter only worked when manually shifted, on several occasions.  When it was under warranty, they told him it was a computer reset, and in a short time, the car shifted normally in drive. Now that the warranty is done, they want to charge 90 dollars.  Is the "reset" a simple task, or does it require unique shop equipment?  Does this occur because of his driving habits?  They also mentioned the throttle sensor...that may have been a coincidence.

Answer
There's more than a computer reset involved.  Reset simply implies clearing the diagnostic trouble codes and perhaps clearing the learned adaptive values.  This won't solve your issue unless the problem causing the code to set in the first place is repaired.  

It's possible that the throttle position sensor (TPS) is causing your transmission problems.  The transmission control module (TCM) uses input from the TPS to help determine when to shift.

Clearing the trouble codes can be accomplished by disconnecting the battery, but again, this won't fix your problem.  Furthermore, if you clear them yourself and then take the car in for service, the service facility won't be able to determine what the problem may have been because the trouble codes have been erased.