Hyundai Repair: 2001 Santa Fe jerking at highway speed, transmission control module tcm, transmission control module

Question
My 2001 Santa Fe (2.7 4 cyl automatic 102K miles) started jerking forward at speeds between 55-62mph.  This doesn't ALWAYS occur, just occasionally but is progressively occurring more often.  After the jerk occurs (hard jerk like someone is hitting you from behind and only ONE jerk), the car drives like it would feel if you were driving a manual at 60 in 3rd gear.  When i pull over and restart the car, the problem goes away and the car drives fine....as if it resets itself.  It actually drives very smooth and like new.  I've noticed today that at times it is very very "slightly" sluggish during stoplight take offs.  Also a problem is the engine light being on...but this has been a reoccurring problem that noone has been able to answer and i usually get the "its the gas cap" answer or I've noticed it will come on after a trip through the car wash.  Today a tech told me that the problem was fixed (the jerking) b/c of a sensor that had to be cleaned.  Once i got in and got 5 miles away, the jerk occurred again.  The Tech is telling me over the phone that he now needs to replace the sensors because that is what the diagnostic originally indicated.  One week ago the same tech changed the transmission fluid and indicated the transmission looked fine.  After reading various problems like this one on this Site with getting a sensor replaced with no guaranteed fix, is there anything else that may be causing this problem?  My timing belt and converter were replaced 3 years ago.  Thanks for your time.  jm  

Answer
Not knowing the diagnostic trouble codes present in your engine and transmission computers, it's difficult for me to give you a likelihood that the sensor will repair the issue.  But your description of the issue makes it sound like the transmission control module (TCM) is placing the transmission in failsafe (third gear only) and requesting the engine control module (ECM) to turn on the check engine lamp.  In that case, the check engine lamp should typically come on when the jerk occurs.  Of course, if the check engine lamp is already on for another reason, it won't be able to indicate that there's an additional problem.

I've not known of cleaning a sensor to solve a check engine lamp issue.  If I had to guess based on what you've stated, it sounds like you had a problem with either your input speed sensor or output speed sensor, and since cleaning it didn't solve the problem, the mechanic now wants to replace the sensor.  

Diagnostic codes do not tell mechanics to replace a component.  They simply tell the technician what sort of problem was seen by the computer.  I suspect in your case, for example, that the computer intermittently receives no signal from either the input or output speed sensor.  The technician then has the task of figuring out whether the problem is with the sensor, the wiring between the sensor and the computer, or even in the computer itself.  I can say, that codes for the input or output speed sensors are almost always triggered by a failure within the sensor itself.  I think I can recall only one case on a transmission similar to yours that such a code was caused by something other than the speed sensor in question.