Hyundai Repair: 2001 Hyundai Accent transmission problem, transmission control module tcm, transmission control module

Question
Hello. I have a 2001 Hyundai Accent hatchback with automatic transmission which I bought brand new in December of 2000. I have maintained it to the letter and there is now 117 000 km on the car. I have had no issues with the vehicle until this problem surfaced a few months ago. Sometimes while driving I can feel the transmission shift down and it will not shift back up into high gear. When this takes place and I come to a stop the transmission often will not have shifted in to the lowest gear so that when it is time to pull away it has no power to pull away normally. If I shift into '2' manually then it will be better but it is definitely not normal. If I turn the engine off and restart it immediately then I have both my high gear and my low gear back but the problem could arise again in minutes or not at all. This happens very frequently so I am wondering if it has happened to others with the same vehicle as well as there were many made and sold. Have you any idea what the problem might be?
Thank you.  

Answer
The symptoms you describe simply indicate that the transmission control module (TCM) has put the transmission in what is called failsafe.  This will occur when the TCM sees any one of a number of different problems.  And when this occurs, your check engine lamp should illuminate and a diagnostic trouble code (DTC) should be stored in the TCM.  When you turn the vehicle off and restart it, the TCM will operate the transmission normally until it witnesses the problem again.

It's the DTC in the TCM that is the key to beginning the process of determining your issue.  If you read the DTCs from your TCM and follow up with them here, I can advise you on how to proceed with diagnosis and/or repair.  AutoZone and AAMCO have advertised they'll check DTCs for no charge.