Hyundai Repair: 2000 Hyundai Elantra auto stuck in 3rd gear, hyundai elantra, transmission control module tcm

Question
QUESTION: My Hyundai elantra automatic, has a problem after it warms up, IT will not engage into forth gear. Stays in 3rd on highweay speeds. When I come to a stop it stays on 3rd, and doesn't go back into 1st gear. Until it cools off there is no way it will shift. A CEL light came on, The code that it spits out is "p0734:Incorrect 4th gear raio". I replaced all sensors that I could see on the outside. Replaced fluid. Flushed tranny cooler. Same exact problem. Any help will be trully appreciated,

ANSWER: Hi, Mike.  I'm afraid I don't have good news.  If the only trouble code you're receiving is P0734, the most likely scenario is that you'll need to have your transmission overhauled or replaced.  What is occurring is that the transmission control module (TCM) is detecting slippage in fourth gear.  (If you can feel this slippage prior to the transmission shifting back down to 3rd from 4th, this further suggests you indeed need major transmission repairs).  When this slippage is detected, the TCM will put the transmission in 3rd gear until the ignition is turned off.  This is because without doing so, it may be unable to operate the transmission well enough for you to drive the car.

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QUESTION: Thanks for the quick response. I was afraid so too. The car only has 79K miles. I've done some research I found out that End clutch may be causing this. Is it true - that I don't know, If I knew what it looked like or where it is I might be able to save this tranny. Afterall, overhauling should be my last option.

Answer
If we go back to the 1994 model year or so, I'd fixed many transmissions slipping in only fourth gear by replacing the end clutch.  As the transmission designs changed with the advent of the 1995 Accent and 1996 Elantra (very similar to your 2000), the end clutch fixed so few that I'd stopped trying.

If you want to try this, I do believe you can purchase the end clutch assembly and service it with the transmission in the car.  It's located just inside the cover on-- you guessed it-- the end of the transmission.  You may need to unbolt the transmission mount to get the transmission low enough to get the cover past the frame rail, but at that point you should be able to remove the end clutch and install a new one.  Still, considering the expense (the end clutch assembly, as I recall, was around $250 in the mid '90s), this is an expensive guess that isn't likely to fix your issue.