Transmission hard downshift.

[LankyGap]

Fluid level is probably wrong - need to verify the AT fluid temp before pulling the check plug. It is different than the engine coolant temp.

https://static.nhtsa.gov/odi/tsbs/2016/SB-10081115-0699.pdf

I doubt it, as I also measured precisely...

 

[Greasymechtech]

Quit with your foolishness

Your precise measurement is meaningless, and borderline trollworthy.

Get a scan tool. Check the level at the proper temp per the procedure. Should overfill it by a pint and let that excess drain out.

And, you should should reset any learned adaptive parameters with the transmission.

My Hyundai 6 speed had wiring harness and sensor problems. So, I would verify your specific year/vin range for any tsb's, recalls, hardware and software upgrades. This will require a trip to the dealer if you're not capable, which I will assume since you didn't check the level correctly.

 

[The Critic]

I doubt it, as I also measured precisely...

You’re assuming that the original fill was at the correct level. It isn’t always. If you performed the level check when the temp was too high, you likely have an underfilled transmission

 

[LankyGap]

Quit with your foolishness

Your precise measurement is meaningless, and borderline trollworthy.

Get a scan tool. Check the level at the proper temp per the procedure. Should overfill it by a pint and let that excess drain out.

And, you should should reset any learned adaptive parameters with the transmission.

My Hyundai 6 speed had wiring harness and sensor problems. So, I would verify your specific year/vin range for any tsb's, recalls, hardware and software upgrades. This will require a trip to the dealer if you're not capable, which I will assume since you didn't check the level correctly.

I used my scanner to reset the adaptive shift. After a vigourous test drive, the problem is gone. I did not expect that result. Time will tell, but yesterday I could reliably reproduce the hard downshift at a precise speed, and after the reset I could not once reproduce.

I found the ATF temp sensor in car scanner, I will redo the level check procedure.

Two important questions....

1. Where did you get that procedure doc like that so easily? I want to be able to do that.
2. How do I use my VIN to check TSB, recalls, and hardware / software updates?

 

[JMJNet]

Did you put enough fluid on the fill?
I had something like this happened in the past because there is not enough fluid during the fill.
It may be only a pint or so.

 

[GSCJR]

reset any learned adaptive parameters with the transmission.

I once resolved an issue I had with an older Hyundai Accent by doing exactly this. The only difference was it had a hard 1-2 upshift and a fluid exchange did not help.

 

[dumkid]

my car does this same thing, but it's tranny mounts or differential/cv axle play. ill get new transmission bushings someday....

 

[SubieRubyRoo]

I have a 2015 Hyundai Accent with a 6-speed auto transmission. I just did two drain and fill with maxlife, but I am pretty sure this has occured before that, and now I am just really focused on the problem.

The transmission shifts smooth almost all the time. But at certain speeds , if I completely completely dxepress the throttle from like 0%-100% rapdily (essentially stomp it), the car downshifts very hard with a thud that reverberates throughout the body of the car.

For example, if I drive along at 40kmh with the rpm at like 1500, in 4th gear, and throttle just barely pressed to maintain speed, and then immediately mash the throttle, there is a very abrupt thud / impact in the tranmission before the downshift. I have never experienced this is a auto transmission before.

What could be causing this, and it this a sign of transmission failure?

Did you clear/reset the fuzzy shift logic? Not familiar with Hyundai transmissions whatsoever, but there are plenty of instances where people with Fords (myself included) changed the trans fluid and had some shifting issues that were then resolved after clearing the previously learned behavior.

You should be able to find how to do it on the internet; it’s usually nothing to do with the fluid itself, unless you’re pointing the finger at the old, dirty fluid.

 

[LankyGap]

Did you clear/reset the fuzzy shift logic? Not familiar with Hyundai transmissions whatsoever, but there are plenty of instances where people with Fords (myself included) changed the trans fluid and had some shifting issues that were then resolved after clearing the previously learned behavior.

You should be able to find how to do it on the internet; it’s usually nothing to do with the fluid itself, unless you’re pointing the finger at the old, dirty fluid.

As stated a few comments up, this was the solution. I can't believe resetting the values solved such a pronounced issue....