Hi, I have a 2.5l V6 4speed Auto. When driving the trans will drop back into 3rd and stay there, when you slow down to a stop and take off it's still in 3rd. But if i stop the car turn it off for a while its ok, till the next time, any Ideas?

 

How many miles do you have?
When was the last fluid change? Fluid flush?
Did you do a trouble code scan?
What condition is the fluid in?
Is there the correct amount of fluid?

 

You need to get it scanned. If it is going into 3rd gear failsafe but resets after turning the car off it is electrical. probably a input or output speed sensor.

 

Howdy. Brought the car to a mechanic who scanned the trans and came up with a faulty output speed sensor .Now iv'e had the car 9 years (120,000km)and it was just getting on to 5 years when this problem 1st occured and had the sensor replaced and fixed the fault till now, so i decided to go and just put a new sensor in. Two days later problem back again. Only thing is im not too sure now if the mechanic said it was the input or output sensor( will find out today) If it is the output sensor then i will get a free one under warranty from the dealership i bought the last one from cos its only 3 months old.If its the input sensor i'll pay for that one.

 

Hi, it is the Input sensor and i'll be getting it changed this Tuesday 10th March hope it goes OK!

 

Sounds like the dealer owes you a new sensor anyway since he misdiagnosed the problem the first time

 

Iv'e finally had the Input sensor replaced and so far its been going great. The first time I had the problem I brought it to the dealership and had the Output sensor replaced under warranty. A few years later (Last Nov/Dec) It started going back to 3rd so i thought right its doing the same thing i'll get another output sensor put it in and the same problem was still there. Thats when (with the current fault) that i took it to a different dealership (20 kms closer) they scanned it and told me it was the INPUT sensor, so I couldnt get the 2nd output sensor replaced under warranty because that wasn't the problem. Any way it always dropped back into 3rd driving 25kms to work and also coming home again, I have done this 3 times and it's still going great. I really hope that the problems been fixed.

 

Hurray for you! Good going.

 

Howdy, the transmission is fixed so far it hasnt changed back, you know that feeling in the back of your head that it could do it any second! With these input/output speed sensors it seems to be a very common problem with Hyundai/Sonata's, especially checking on the net and this forum, has Hyundai ever had a recall? am I wrong to assume this, thanks

 

I have a 2000 Hyundai Sonata that was showing the same symptoms with its transmission. I took it to Auto Zone for a free diagnostics test. I discovered just what this site was saying and that is either the input or output speed sensor is bad. The reading showed the input speed sensor was bad.
I wanted to purchase the sensor and install myself but my time was short so I let the dealer do the work for 461 and some change. I want to thank this website and all the comments about this problem. I will repost if the part fails and or the symptoms return.