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I also have this kind of bump feeling, but not always. I'll ask the dealership to check out if there's anything wrong about the transmission.
Also, when cold, on my case, the first shift between 1st-2nd is slipping more or less, I have to let it shift with light throttle @1.5k rpm.

I've been searching about the 8spd sedona/sorento, looks like there's something about this transmission. Hope Kia will fix it by ECU or TCU update.
 

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I heard of the same flare on the first shift in the original 8 spd transmissions from 2006 (lexus), it might be a thing with 8spd trannies.
 

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2018 Kia Sedona EX US
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That feeling you describe is the programming in the transmission shift logic. I’ve been to the dealer a few times and until more people complain of it Kia won’t release new software for it. There was even a large discussion on it on the Sedona Facebook page. After dealing with it and getting aggravated that the transmission hesitates to downshift in partial throttle I looked into it. Turns out our gas pedals are adjustable, and it seems to prevent jerkiness Kia adjusted it on the lazy side this causing the engine to lug and have that missing feel. I adjusted my pedal, at around 8k miles to get rid of the dead space and for the transmission to downshift when you press the pedal more than 1/4 down the van is now responsive and am now at 29k miles and haven’t felt the hesitation ever since.

I followed this guide to doing it, same conceptdifferent Kia/Hyundai model. The pedal sensor assembly is the same except in the van instead of being floor mounted it’s mounted to the firewall.https://www.hyundai-forums.com/threads/getting-rid-of-the-dead-space-in-the-gas-pedal.170185/
 

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2020 Kia Sedona EX
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1 Posts
I have the exact same problems with my brand new 2020 Kia Sedona EX. It started doing it before it hit 1000 miles. Only had it about a month. I took it to the dealership and they told me it drives fine. The mechanic mentioned that Kia Sorrento is known to have this problem but seemed to be surprised I had it going on with my Sedona. At the time I did not realize how many people were having problems with this. Apparently it is a problem with Sorrentos and Sedonas. I saw on this forum a ton of complaints and good info from Sorrento owners concerning the very same issues.

My suspicion is that both vehicles use the same components so they both suffer from this defect. The thing that is crazy is that sometimes my van will do almost perfect and other times it hesitates terribly and shifts very poorly on hills. It basically tries to ride in high gears when it should be in a lower gear.

I have done some experiments and changed to manual when it is struggling and noticed that it jumped into high gears too early for the speed I was going. For example I have seen it go into 8th gear at 35 miles per hour. The symptom of "road noise" or "bumpiness" is very similar to the feeling you get when you put a manual transmission into a high gear when you should still be in a lower gear. My Sedona will basically skip lower gears too soon when its having a bad day and that is why it seems to get that lugging or shuttering feeling to it. Its trying to ride in a higher gear when it really needs the lower gears to get momentum and move the weight of the car.

I know this may sound strange, but I think there are environmental factors influencing this whole problem. I need to do some controlled experiments, but so far it seems that rain and high humidity make the problem worse. I have heard that some people don't have problems with it when it is below 50 degrees outside and it returns when the warmer more humid temps return. I still need to really pay attention to this but it does seem to be true since we have been getting a lot of rain where I live and its been extremely humid and the van has really been acting up this week. I also had a cooler and real dry day about a week ago and noticed the van rode smoother and shifted normally using the correct lower gears based on the correct speed, so that is why I think there may be a connection with the environment. Perhaps a sensor if getting wet or too hot?

Who knows at this point. Maybe it is a solenoid problem. I found this website (Kia Sedona: Troubleshooting - Automatic Transaxle System - Kia Sedona YP Service Manual) which seems to be a reproduction of the service manual and it seems to point to either a damaged clutch/brake, a faulty hydraulic control, or a faulty hydraulic supply. One of the remedies says to Inspect the solenoid valve. I am wondering if the solenoid is "sticking"?

I am not a mechanic, but doing a little research shows that solenoids can become "sticky" if they are not manufactured correctly. See this discussion: Transmission Problems With New 2010 Santa Fe. Someone by the username of "canderson" wrote something very interesting:

"Again, it's all been conjecture, but early on in this problem, there were rumors about an anodization problem causing the solenoids to stick in the valve body. Unanodized aluminum is quite soft and 'sticky' and wears quickly with repeated friction of motion. When a solenoid would stick, you'd essentially have an attempt to engage two gears at once, causing the bump. The way transmissions are designed now, timing is everything with simultaneous actuation/de-actuation going on, and binding for any reason isn't tolerated in the design."

Although the above quote is referring to issues with a Hyundai (Kia's twin company) vehicle other than the Sedona, I am suspecting that that quote may be applicable to what people are experiencing with their Sedonas especially since Kia probably uses Hyundai parts interchangeably. My other suspicion is that somehow weather and temperatures are playing a part in this whole thing. Perhaps the environmental factors are causing just the right moisture/temperature combinations to fowl up whatever sensor/mechanical relationship is going on when the car is shifting?

If anyone reading this is a mechanic I would love to get your input on this whether or not this sounds like a reasonable explanation for what might be going on. Like I said I am not a mechanic, and I don't even know what a solenoid is. Lol!
 

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2019 Kia Sedona
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I haven't brought mine in yet, but j have the same issue with my 2019. We bought it used at 52,000km and we have about 3000 on it since then. I'm curious to see what the have to say.
 

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I did have a very hard shift once with my six speed... the bumb was pretty scary and the ECU seems to have not understood what happenend either... I thought the engine had seized just like that, but I laid my foot off the gas and it could accelerate back normally a second after :O
 

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102 Posts
I've grown accustomed to turning right or left onto the next street, only to find my accelerator pedal slow-to-respond.

It bothered me at first, but nowadays, when I complete those turns, I wear some patience and do not push the accelerator pedal to passing gear, in an effort to speed up quickly. Instead, I just let the engine slowly gain MPH, instead of quick-gains.

I've never had an issue with how the engine responds from stops (red lights). My power is fine there.
 

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My 2021 was fine until about 200 miles. Now it obviously shows signs of transmission shudder. I set an appointment with the dealership to have it looked at and they said it needed about 500 miles to " learn how I drive". At 1100 miles I took it in because there wan no improvement. They said all normal and it needs 5000 miles to learn how I drive. Of course this is nonsense. I'm going to take it back at 5000 miles and keep the documentation going. If no improvement I'll just lemon law the thing. The idea that transmission shudder is normal is simply idiotic.
 

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99 Kia Elan 1.8L
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My 2021 was fine until about 200 miles. Now it obviously shows signs of transmission shudder. I set an appointment with the dealership to have it looked at and they said it needed about 500 miles to " learn how I drive". At 1100 miles I took it in because there wan no improvement. They said all normal and it needs 5000 miles to learn how I drive. Of course this is nonsense. I'm going to take it back at 5000 miles and keep the documentation going. If no improvement I'll just lemon law the thing. The idea that transmission shudder is normal is simply idiotic.
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I’m at 3700 miles and for now the issue is gone, but I’m wondering if that’s because here in Canada they switch to winter gas at 15 september. The issue went away during september. Was bad in august.

For my case: My transmission always do a shift flare (cold/warm) between the first and second gear, I can’t just do a quick acceleration from 0mph, have to leave it shift by itself below 2k rpm, waiting to be more serious, the dealership said it is within Kia specs, oil level is fine.
 
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