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Discussion Starter #1
When I'm slowing gently to a stop, the car gets down to about 10 mph, and then the brakes seem to suddenly grab. Any ideas?

Been going on a while on my new-ish 2018 Sonata SE, 8500 miles. Thing is, its intermittent. Really only one time in 10. I can't seem to figure what conditions to reproduce it. I took it in, and of course, could not reproduce the problem. Google search didn't turn up much. Seems to happen when I glide gently to a stop, not when I stop more forcefully.

Would appreciate any ideas!
 

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You sure it’s the brakes and not the transmission downshifting? I mean, improperly-adjusted brakes from the factory isn’t rare but it isn’t common either. Bring it to the dealership you got it from, and have them take a look.
 

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Discussion Starter #3 (Edited)
You know, the feeling is in fact like a transmission downshift. If so, what to do? Any one else got this? That when you're gently braking to a stop, around 10 mph the stop gets suddenly strong. I just wish I had a reliable way to reproduce the issue. I'll try switching between the drive modes. And yes, I can take it to the dealer, though I wish I could demonstrate it reliably.

Hrm I found a similar sounding problem https://www.carcomplaints.com/Hyundai/Sonata/2018/transmission/hard_downshifts.shtml
https://www.hyundai-forums.com/sona...4-cyl-transmission-jerks-when-downshifts.html
 

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My Tucson does the same thing.
At ~20mph it downshifts and brings rpm to ~1500.
 

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Discussion Starter #7
A feature not a bug...

I talked to Stevens Creek Hyundai service. Their service department advanced the view that this was normal. That it was, shall we say, a feature not a bug.

I'm glad its not the brakes. I'm glad I'm not the only one with it. I'm glad the powertrain has a limited warranty for 10 years and 100,000 miles.

Its possible that Hyundai, like Apple up the road from this dealership, when there is a real problem they shine you on and deny it for a while.

I will say that I've never had a car behave quite like this. And I'm not sure if any of the 3 driving modes change it. Its fairly intermittent, and I haven't yet figured out a way to make it happen repeatably.

In my case its not a hard downshift, and there's no problem on the upshift. So I am just going to wait and see. I've got 9 more years to see if my personal, or the collective owner experience, triggers a fix.
 

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There is a recall for this issue. Your TCU (transmission control unit) needs to be reflashed by the dealership. Took mine 2018 in for an oil change and they went ahead and did it. Haven't had the issue since.
 

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... Your TCU (transmission control unit) needs to be reflashed by the dealership. Took mine 2018 in for an oil change and they went ahead and did it. ...
Was that for the 6-speed or the 8-speed?
 

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I was having the exact same issue on my 2018 Sonata SE. I was able to reproduce it by the folllowing:
- Be in ECO or COMFORT mode
- Get up to 18-20 MPH
- Coast or brake slowly down to 14MPH
- Get a lurch as the car does an ugly downshift

It never happened in sports mode.

In any case, last Friday I took it in and they said there is a service bulletin on it, they had T3B listed on the invoice with the words "shift lock." In any case, they did a TCU update and my car drives perfectly now! Hope this helps someone as it is so frustrating when it would happen.

gaz
 

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Discussion Starter #13
1. This is the only car I've ever driven in my life that behaves this way
2. Its not normal
3. It is rare though
4. This thread, and some of the links in it, show that some people do have this
5. Its not the brakes, its downshifting
6. Doesn't happen every time, but it can be reproduced

I'm due for my 15,000 mile service. I'm not going to let them gaslight me like they did last time.

If anyone knows the service bulletin I'm interested. This website says it can find all TSB's https://www.carmd.com/wp/lp/technical-service-bulletins/
 

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If your local dealer doesn't help, check the yellow pages and drive to the next dealer further down the road.

I am a bit surprised as the issue has been around for a while and most dealer services will include ALL campaigns and recalls. If this is a TSB, then they should update software with any owners complaint.

Since service writers are idiots, I would talk to tech that drives vehicle in and verify with him that you have the latest software, and that all recalls and product improvement campaigns are completed.

My favorite day at dealer is when I printed out a TSB and left it on the front seat for the tech. Yes, the couldn't find the TSB for the issue I reported, even though it was pretty common. I told the tech to read the papers on the front seat. Forking rocket scientists... NOT!
 

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Discussion Starter #15
Open Campaign

I talked to a service technician ahead of time just now. They might have picked it up anyway, but I didn't want to take any chance. They plug in my VIN and found 2 "open campaigns". First was the engine firmware update, second was the T3B firmware update, which I think is for the TCU "transmission control unit". Said it takes another 45 minutes. I assume all this is covered by the warranty. So hopefully next week after the appointment my car will also drive perfectly. Thanks gazibidian, and the forum!
 

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Discussion Starter #16
I just got back from the Hyundai service. I didn't get a copy of the paper I signed, but they did say when they run my VIN, there is a "service campaign" for the transmission. And indeed on the drive home it indeed appears this problem, for which I started this thread, is fixed.

They also did the engine knock-detect firmware upgrade, for which I got a recall notice (did not get one for the transmission). And sure enough, just as I'm getting home, well the good news is that firmware update is in and working. The bad news is I know this because, as the service rep said happens only 1% of the time, now the check engine light is blinking, and the car won't go over 2000 rpm. Of course, she also told me that the knocking I complained about and noted when I brought the car in, was probably caused by the acorns and rocks a squirrel had put under my engine cover rattling around. True story. Yes, debris from a squirrel, and yes, that was their explanation for the knocking. But now that at 15,000 miles I have the new ECU firmware, it immediately detected that yes the knocking was part of the recall. I'm sure I can find other threads about this, and that I have excessive bearing wear. They do extend the warranty to 120,000 miles.

However, in light of all the above, soon I will stop using this Hyundai dealer in San Jose for my repairs. And its hard to justify buying another Hyundai in the future. Things shouldn't go this wrong in the first 15,000 miles.
 
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