Hyundai Repair: Transmission stop shifting, transmission control module tcm, transmission control module

Question
as im traveling down the road (usally on the freeway crusing with light pedal pressure), the trans will down shift out of OD and the check engin light will go on. the car at that point will not shift out of third. once I pull over and turn the car off for a few seconds, restart , the light will turn off, and the car will shift again just as normal. I have had several mechnics look at if and every time they check the error history if give them a different reading? The last mechanic (i actually trust this one) says the ECM needs to be refalshed? So my question is how do you check the ECM or ECU to make sure that is the problem? and Wich one is the problem the one for the drive train othe the one for the trans?

Answer
There is a problem seen by the transmission control module (TCM).  When it sees this problem, it requests your engine control module (ECM) to turn on the check engine lamp and puts the transmission in third gear.  When you turn off the car, the system reverts to normal until it sees the problem again.

To determine the problem, the first step is to read the codes from the ECM and TCM.  This will tell us the nature of the issue.  Then, depending on the codes, additional diagnosis can be done to pinpoint the actual issue.

If you can tell me the codes that are stored in the ECM and TCM and the year and model of your car, I can probably give you information about what your problem is or how to diagnose it.