Hard downshifts

[Larry P.]

I will try my best to explain this with detail.

I don’t know if this is just my car or a problem within a lot of stingers. When I am driving in automatic, on any mode, my car downshifts harshly at times. When I’m braking, as well as when I’m letting it coast to a stop. 7 times out of 10, the downshifts jerk my body forward a little bit, especially when then car is going from 3rd to 2nd gear, 2nd to 1st gear. At first I was thinking it could probably be torque, but it feels so different than downshifting with the paddle shifters.

When I’m controlling the gears and using the paddle shifters, I feel like body jerk can be normal depending on what the rpm’s jump to after a downshift, and I have no issues.

I have no indication on what this could possibly be. Or maybe I just don’t understand my own car. If anyone has heard of this, please point me in the right direction.

 

[Plakchup]

This is fairly common on the stock tcu. I had it happen on all 3 stingers I've had. There are basically two solutions.

1. Get xtool anyscan obd2 scanner and reset the transmission adaptations. This will help with the harsh downshifts but eventually it will happen again and you will need to repeat the process. This is what I did initially but I knew I wanted a better solution. Stealerships might reset it for you but you will need to go bug them every few months likely.

Wireless OBD2 Scanner, XTOOL... https://www.amazon.com/dp/B098NC47SX?ref=ppx_pop_mob_ap_share

2. Get a tcu tune, something like the bms tcu bef tune via ek1 or a physical tcu swap like something from lap 3 which is pretty expensive. This is a way better solution overall imo.

I run the bms tcu bef + kjt e30 ecu tune and its butterly smooth in downshifts and upshifts in comfort mode. No more harsh downshifts in comfort and sport/custom, especially that 3 to 2 gears that always annoyed me. The upshifts in sport/custom are more aggressive as expected. Manual shifting is much faster, precise and smoother as well. Probably one of the best modification I've done. Small note that every time you install a tcu mod there is a learning phase it will go through where initially the shifts might be harsh but it will soften as you drive more. I posted a video of how the car drives in the ultimate tuning forum if you want to see.

Link to thread:

P

Thread 'KJT E30 ECU + BMS TCU BEF is fire!!!'

Feb 1, 2026

Going from JB4 only to these 2 BEF tunes is a really day and night difference. Initially all I wanted to do was the TCU tune but learning about KJT's ECU tune really made me more curious with all the benefits it comes with. This combo is exactly what I was looking for. Burbles, better e85 adaption, better overboost management, more power, more torque, no more jerky downshifts from 3 to 2 that I always noticed. Much smoother shifts in comfort. Also very quick and crisp upshifts and downshifts in sport/custom mode. Here are 2 quick initial impression videos I made today. The burbles are the...

• Plakchup
• Replies: 4
• Forum: The Ultimate Kia Stinger Tuning Forum

 

[Black Beast]

Get the scanner! Even if you decide to go with the TCU upgrade, this scanner with its software is 2nd to none. You can do a lot more with it. Software updates are life long so you will always have updated tool. I was having the same issue with my GT2 and now that’s a thing of the past. Very simple to use, there are even videos on YouTube for the device to help you out. Best 100 bucks I have ever spent. I say 100 bucks because I live in Canada. lol.

 

[Larry P.]

This is fairly common on the stock tcu. I had it happen on all 3 stingers I've had. There are basically two solutions.

1. Get xtool anyscan obd2 scanner and reset the transmission adaptations. This will help with the harah downshifts but eventually it will happen again and you will need to repeat the process. This is what I did initially but I knew I wanted a better solution. Stealerships might reset it for you but you will need to go bug them every few months likely.

Wireless OBD2 Scanner, XTOOL... https://www.amazon.com/dp/B098NC47SX?ref=ppx_pop_mob_ap_share

2. Get a tcu tune, something like the bms tcu bef tune via ek1 or a physical tcu swap like something from lap 3 which is pretty expensive. This is a way better solution overall imo.

I run the bms tcu bef + kjt e30 ecu tune and its butterly smooth in downshifts and upshifts in comfort mode. No more harsh downshifts in comfort and sport/custom, especially that 3 to 2 gears that always annoyed me. The upshifts in sport/custom are more aggressive as expected. Manual shifting is much faster, precise and smoother as well. Probably one of the best modification I've done. Small note that every time you install a tcu mod there is a learning phase it will go through where initially the shifts might be harsh but it will soften as you drive more. I posted a video of how the car drives in the ultimate tuning forum if you want to see.

Link to thread:

P

Thread 'KJT E30 ECU + BMS TCU BEF is fire!!!'

Feb 1, 2026

Going from JB4 only to these 2 BEF tunes is a really day and night difference. Initially all I wanted to do was the TCU tune but learning about KJT's ECU tune really made me more curious with all the benefits it comes with. This combo is exactly what I was looking for. Burbles, better e85 adaption, better overboost management, more power, more torque, no more jerky downshifts from 3 to 2 that I always noticed. Much smoother shifts in comfort. Also very quick and crisp upshifts and downshifts in sport/custom mode. Here are 2 quick initial impression videos I made today. The burbles are the...

• Plakchup
• Replies: 4
• Forum: The Ultimate Kia Stinger Tuning Forum

Your car sounds amazing man. I will definitely look into the xtlool scanner for now. I’ve never had a device like that scanner, and I’m sure there are videos out there to help, but is it user friendly?

 

[Larry P.]

Get the scanner! Even if you decide to go with the TCU upgrade, this scanner with its software is 2nd to none. You can do a lot more with it. Software updates are life long so you will always have updated tool. I was having the same issue with my GT2 and now that’s a thing of the past. Very simple to use, there are even videos on YouTube for the device to help you out. Best 100 bucks I have ever spent. I say 100 bucks because I live in Canada. lol.

That scanner is $650 in the US, so I’ll hold off on that until I do some research on it. Down the road, this will be a great possibility for me.

 

[Black Beast]

The scanner is very easy to use, self explanatory. I have mine paired to my iPad. You can pair to a laptop or phone device through the software, I can only attest its simplicity using Anyscan software for IOS. But I’m certain it would be just as simple for any. Hey, for 80 bucks how can you go wrong. It won’t only fix one issue and you can use it on nearly every vehicle that came out with a ODB2 plug. Just think, you can even diagnose BMW’s and McClarens Lamborghini’. Etc. lol

 

[Black Beast]

Get the A30D scanner, it’s all you need. Doesn’t come with its own screen but you can Bluetooth pair it to an iPad or whatever your little hear desires. This scanner is 89 dollars US on Amazon. Just follow Plakchup’s thread.

 

[Plakchup]

Thanks! Yeah she's something else now! Might be bit too much power now! But I baby her often and just enjoy the fine tuned driving experience more in general. Haven't been brave enough to go WOT yet lol.

Here are my instructions I posted on reddit. The scanner tool is great and usually is on sale. Handy tool in general if you do not want to flash your tcu.

"Turn car engine off

Turn on ignition (press ignition button twice without your foot on the break pedal. You should not be in "accessory" mode.

Plug in the XTool and connect to Bluetooth (assuming you've already gotten BT pairing, the app installed on your phone and established all connectivity already)

Select Special Function in the app.

Find the Gearbox Match menu.

Select car make and auto detect.

Reset gearbox learning option.

You might have to select the 2020 or 2022 year stinger. The transmission is the same. I updated my xtool (took a while) and i was able to select the 2022 stinger option. Did the reset. Turned ignition off. Let it sit for a good 30 secs or so. Turned on and went for a drive. Immediately noticed the smoother shifts in comfort. Sport/custom mode is pretty much perfect now too; crisp and quick shifts and proper downshifts with rev matching if you are slowing down bit faster. Also noticed very smooth gear changes from P to R to D. Like so smooth you don't even feel it.

I was a bit confused in the app to pair the Bluetooth. I kept trying to pair it on my phone but you have to select it in the app actually the xtool itself. That's all."