I have a 2004 Hyundai Sonata LX auto transmission. Just recently it started downshifting even during a maintained speed. It happened during city driving where I may be going 25 to 30 miles per hour and it would shift down from 3rd to 2nd and my RPMS would rev up to just under 3000. This happened both when starting out from a stop light (then it was going from 2nd to 1st) or a constant speed. I decided to use the manual shifting and the car behaved much better. However I did notice that while highway driving it shifted from 4th to 3rd on it's own. My son thinks it may be the ATCM. I checked the cost with my local Hyundai dealer and it is around $870. At this time of the year that is a big ouch to my budget. Would anyone be able to tell me if this may indeed be the problem, or if there is possibly an easy fix that I may do myself?
SOURCE: Using the select shift in my 2009 sonata
The purpose of shift tronic is to give the driver the option of driving like a manual where you command the shift, or auto for easy driving (little effort). It is not specifically used just to down shift or upshift. When you are in 5th gear, thats it, it will do in it normal mode or sport shift.
SOURCE: I bought a 2000 Hyundai
The input and output transmission sensors may be bad. My car had this malfunction. I replaced the sensors and have had no more problems.
SOURCE: transmission/shifting 2001 Sante Fe - Hyundai
Sounds like you might have serious internal transmission problems.
As soon as you can, get someone with a code reader to plug in the vehicle and find out what the code is for the Check Engine light to come on. Might give you a better picture of what`s going on.
It could also (cross your fingers) be something more usual like a clogged transmission filter (located inside the pan), or shift solenoid.
By the way, have you checked the level, look & smell of your transmission fluid?
Level should be checked with the vehicle running, after passing it in all gear ranges on the shifter, and putting it back in park (Check it on "cold" or "hot" level depending on if it`s been driving for a while or not).
As for look and smell, it should be reddish and not smell burnt. Hard to describe the smell of burnt transmission fluid, but normal fluid does not smell too strongly, kind of sweet. Burnt oil is usually black and has a strong odor. If the oil is burnt you have internal damage to the transmission.
One piece of advice I give you is get it fixed as soon as possible because if you don`t already have serious internal transmission problems, the longer you wait, the more chances you have of getting some, to the point of the vehicle just refusing to move. And believe me, speaking from experience, the transition point from the symptoms you describe to total refusal to move and the need for a tow/transmission rebuild is not that long usually.
SOURCE: i have had my tiburon less than a year but about a
the trans computer has seen a problem possible a bad sensor, or an internal problem, and puts it into a safe mode, or limp home mode , it wont shift , it will stay in 3rd gear, this way this reduces the possibility of further damage trans damage, when you turn the ignition off and back on it resets the tcm, my advice is to take it to your local dealer, they can diag your trans as they know the product, i dont advise pep boys, or discount auto parts.
SOURCE: 2008 Hyundai Accent problems
I had a similar problem with my 2008 accent, I took it to the dealer a couple times before they noticed the engine had shifted slightly and had to be aligned and tightened down properly. It has stopped the transmision shudders completely.
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By the way, I did check the tranny fluid and it is normal reddish color with no discernible odor.
I finally fixed the problem by changing the input and output sensors. Since there were no codes, I went ahead and changed them both out. That was back in March 2014 and have had no problems since. Hope this helps anyone else experiencing the same problem.
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