It's supposed to do that, i forget why but the manual explains it. It shouldn't feel like a huge sudden jerk but it is a noticeable downshift

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I face the same issue on my 2018 Sonata. It is a transmission issue. Go to Hyundai service to upgrade a new one.

 

I have / had (?) the same issue, the service tech messaged me that it was a Software problem that was resolved with an update. Really cannot say if the issue has been resolved as, the dealer has had my vehicle for almost 3 weeks for a "co-morbid" problem https://www.hyundai-forums.com/sonata-all-hybrid-models-yf-lf/642663-new-car.html


Seems to be a common concern with the automatic transmission.

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I am facing the same issue. At slow speeds (10-15 mph) while coasting, the engine suddenly jerks and I can feel and hear it very well. I guess it's the transmission and I need to take it for service. Started having this more often after 14,000 miles. Currently at about 16,500 miles.

 

What you described isn't out of the ordinary (I've had a '13 since January of '14).

What is out of the ordinary is when slowing from about 35mph, just as it wants to upshift, and the car goes into panic stop mode and locks up the wheels (antilock braking FAILED) and you leave chirp skid marks - just pray the person behind you isn't too close and is paying attention. And hope you aren't holding a cup of coffee in your hand!

This has happened to me four times in 40k miles.

 

Same trans issue in 2011 sonata hybrid

This is exactly what my trans is doing now. I just installed a salvaged trans to replace the blown one (at 108k). Now the car lurches on stop under slightly harder braking. I'm afraid it's going to throw me into an intersection.

 

'13 HSH here, and I get the same thing, usually either 3rd to 2nd, or 2nd to 1st when slowing down for a red light or stop sign. Not ALL the time, but definitely noticeable.


I'll contact my dealer (I'm due for an oil change/rotation anyway, i'll have them look at it with that)

 

All the hybrids with 60-80,000 miles are due for an fluid change. Hopefully the right type of fluid. Even try for a synthetic fluid if acceptable.
Anyone experiencing hard downshifts may also try the manual shifting for a few miles.
Shift up, then shift down, or not. Its to get the computer to try another aspect of its programmation.
Unfortunately these transmissions don't have dip sticks to check the fluid levels.

 

We have the same problem with our 2009 Sonata. It is also a 4 cylinder automatic transmission. We took it to the Hyundai dealer and they said it needed a new transmission. We had the transmission replaced, and it still was doing the same thing. When we are slowing down at about 20 mph it Jerks. Hyundai said there were no recalls, bulletins or anything else about it. We took it to another mechanic to look at it, and he said the axles and bell housing were leaking. Took it back, had that fixed, but the problem has not gone away. Not sure what to do now.

 

Yours is a 2009, it's better to post in the forum relating to your model year for better responses. Here is a link:
(4) NF (2006-2010) Sonata | Hyundai Forums (hyundai-forums.com)

 

Hi, I bought a Hyundai Sonata Hybrid Premium with 187K kms on it. Soon after buying I noticed jerks while shifting upward and downward from 1st to 2nd gear & also from 2nd to 3rd gear in Automatic mode. I checked the transmission oil, it was dirty so I replaced it. After replacing transmission oil, the shifting from 1st to 2nd got almost smooth but from 2nd to 3rd remained though reduced by almost 50%. I again changed the transmission oil after few hundred kms, this time it showed no change. Anyone who have experienced same issue and got it resolved, please share your experience. Thanks.

 

If it only happens in cold start then that's normal, you can mitigate the issue by cycle through P to D one to two time before drive. If it keep happening when fully warm up you may need to find a mechanic.

 

It happens all the time.

 

Before send it to professionals, try disconnecting the battery (small one on right side of the trunk) and reconnect it after 30 mins, this will reset the vehicle and your transmission will relearn your driving style. If that doesn't help then you may really have a slippery transmission. There are some transmission addictives on market but I'm not sure if it can be used in hybrid or not.