8L90 Logic

[ss4chad]

'17 GMC Yukon XL Denali 8L90 98K miles.
I changed the fluid in the pan with the new Mobil 1 LV ATF HP recommended fluid, I did not drop the pan and change the filter, I changed only the quantity in the pan, about 7 qt's. The dealer did a Trans Service at 72k but they did not know what fluid was used so I tried to make sure the better fluid got into the trans as much as much as possible.
I also changed the cooler flow bypass kit from Superior Solutions.
Still get (sometimes) the harsh 1-2 shift and an occasional 2-3 shift. But, if I shift it manually with the electric trans shift button on the gear shift lever, it shifts as smooth as silk. Could this be a Transmission or PCM Logic issue? Is that trans programable like most of GM's transmissions are?
I can manually shift at 2000-2500 RPM's and it feels like butter shifting, like it should.

Could a Transmission Program be the fix all/end all and not the fluid or the torque converter?
Thoughts?

Chad

 

[Bigkevschopshop]

Honestly, you can reprogram the clutch learning points and it will fix things up alot better. Look into clutch relearn procedures.

I have found it likes a bit of commitment on the small pedal.
A tune would help most likely to get the trans parameters dialed in a bit better also.

Fluid was a major issue GM found enough to do a TSB.

Now not doing filter with the fluid, you have a bit of contaminants stuck there. The fluid temperature makes a big difference also, cold fluid makes them choppy at shifting, too hot of fluid does the same, I have found once driven around a bit the trans calms down with a little heat in it.

 

[ss4chad]

Do I still have to use a tuning software program to make those changes?
HP Tuners or something similar?

Chad

 

[Marky Dissod]

Do I still have to use HP Tuners or a similar tuning software program to make those changes?

Unless you can read and write in binary or hex, yes, you need a tuner's software with a definition file to interpret the changes you're making.

 

[ss4chad]

https://static.nhtsa.gov/odi/tsbs/2019/MC-10169298-9999.pdf

Wow, I was hoping for something a bit easier, this might take a while to accomplish!

Chad

 

[B-train]

Cool bulletin, but yikes! There's a lot going on there. My 8 speed will have it's clunky moments, but I've learned to live with it. Keeping clean fluid has been good. Had the TSB 20qt flush at 43k and services every 40k after. Runs good, I like the trans.