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Discussion Starter #1
I've put about 10,000 miles on my 2015 sonata se 2.4l bringing it to around 40,000 miles now. Lately, while I've been driving and I go to slow down, the car lunges forward and makes a clunking noise like two metal pieces clunking into each other. It happens right around 23-24 mph then happens again about 2 seconds later at 15 mph. I read an article saying that it may just need to be reset at the dealer, but I was just wondering if anyone else has had this problem or has any suggestions?
 

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have you checked your oil recently to see if it's at an OK level?
Funny things happen when engine oil is low, a lot of people don't know their '15 Sonata's are consuming oil.
 

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Sounds like the downshifts from 3-2 and 2-1. Can you confirm on your tachometer that the needle jumps at those moments?


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Hey Matt, checked the oil level and it is right where it needs to be. Haven't refilled it and hasnt been consuming any oil since i've gotten the car.
 

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I would definitely get it looked at if there is a clunking sound. Does it happen every time you decelerate?


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I would definitely get it looked at if there is a clunking sound. Does it happen every time you decelerate?


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Happens at least once every time I drive. I’ve tried it in eco, normal, and sport and it is more frequent in eco, then sport, and the least frequent in normal. I noticed it also happens more when it is warmer out and the A/C is on. A buddy of mine has an 09 sonata and his actually just started doing the same thing. They reflashed the transmission software or something like that and he said it’s been good since. Think I’ll bring it in and see what they say.
 

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Discussion Starter #9
Is it easy to replicate?
How about if used the sportshift mode?


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Happens in sport mode, if I’m using the slapshift it doesn’t do it as I’m in charge of the shifting, but when it’s in the normal automatic mode, it does it no matter what mode it is in.
 

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I haven't had this issue. Doesn't disconnecting the battery and waiting for it to discharge (hold the break ) reset the system? That's what used to work on my older hyundai.
 

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Discussion Starter #11
Took the car to the dealership to have it looked at. They reprogrammed the transmission shift points as they said was a used car and it may have been used to the previous driver. The problem has not happened again yet, but time will tell!
 

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My 2015 sonata is having the same issue, just not nearly as frequent.

It also has major loss of power and hesitation issues, the up-shift points are just way too early and the engine will bog down far too long before it shifts (after I have to give it more gas).

I'm hoping a software reset will fix me up. How long did it take for them to fix it?
 

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You probably need to have the TCM flashed. More than likely the shift parameters need to be widened.
 

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Thanks. I called a local hyundai dealership and asked about this, and they didn't seem to know what I'm talking about. I'll be explaining more to them tomorrow morning, is there anything I can say that may help them? Although I think flashing the TCM should be descriptive enough, and I can even show them this thread if need be.

Thanks
 

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The dealer should be able to look up the VIN in the Hyundai database to see if all ECM and BCM updates have been flashed. We bought our '15 new and it had, iirc, 3 or 4 different flashes performed in the first year.

Drove a LOT better after all were done. Better throttle response, shift quality, that sort of thing.
 

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Turns out a lot of my torque loss and lunges during the deceleration problem was that my variable intake solenoid was completely unplugged. How this happened, I have no idea. But I was covered under warranty and they took care of me. The mechanic explained that it was fudging with my fuel air ratio, since the 'flaps' for the intake were not responding properly. I used to have major power loss on hills and in certain gears. I hope this solves it all for me. Test drove for a bit and seems a lot more fluid in all gears. Will update after a road trip I'm about to take!
 

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Discussion Starter #17
Turns out a lot of my torque loss and lunges during the deceleration problem was that my variable intake solenoid was completely unplugged. How this happened, I have no idea. But I was covered under warranty and they took care of me. The mechanic explained that it was fudging with my fuel air ratio, since the 'flaps' for the intake were not responding properly. I used to have major power loss on hills and in certain gears. I hope this solves it all for me. Test drove for a bit and seems a lot more fluid in all gears. Will update after a road trip I'm about to take!
Glad you figured out the issue, That’s definitely a strange occurrence!
 

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The dealer should be able to look up the VIN in the Hyundai database to see if all ECM and BCM updates have been flashed. We bought our '15 new and it had, iirc, 3 or 4 different flashes performed in the first year.

Drove a LOT better after all were done. Better throttle response, shift quality, that sort of thing.
Did you ask them to reflash the modules for you? After they reflashed my TCM the shifts got smoother, but my throttle response is slow and sluggish. I feel like I have to push the pedal down at least a quarter of the way to get any sort of power out of it. I drive my dads 2014 sonata and it’s a completely different story, and his takes off like a bat out of **** compared to mine.
 

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Did you ask them to reflash the modules for you? After they reflashed my TCM the shifts got smoother, but my throttle response is slow and sluggish. I feel like I have to push the pedal down at least a quarter of the way to get any sort of power out of it. I drive my dads 2014 sonata and it’s a completely different story, and his takes off like a bat out of **** compared to mine.
As delivered new the '15 had very sluggish throttle. After the reflash it was much improved. I did ask them to perform the TSBs. All of them.But there was no push-back as it was a new car and Hyundai had been hearing from many customers that the acceleration was "flat".

Understand that the '11-'14 year model 2.4L has a different "tune" than the '15 and beyond. The earlier 2.4L was considered a bit "peaky" in the torque curve. The '15 and beyond was tuned for a flatter torque curve to improve driveability for the average owner.
 
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