TCM calibration update, service fast learn.

[Crobinson16]

I just got my 2018 Silverado LTZ 6.2 with the 8l90 8spd back from the dealer where I had a TCM calibration update done, it was for improved shifting. They called and told me it was ready for pickup. I read over the work order and noticed that there was nothing listed that said performed service fast learn after installing update. So I asked the service manager and he said he would ask the tech if he did it or not. Service manager said it was not done. They said I can bring it back in to have it done if I wanted no problem. 

I have read over many service bultions pertaining to the transmissions, and they all state that when a TCM calibration update is done that the service fast learn is to be done as well to reset the parameters and shift adaptation.  I've been driving it around for a few days and it feels as though the truck shifts better the more I drive it. When I first drove it home it felt like the tq converter was locked all the time and it didn't want to down shift till the peddle was wide open. The motor would kinda bog for awhile or stay in a higher gear longer before it would shift.

My question is should I still go back and have the service fast learn procedure done. My truck only had 1, 800  miles. If I keep driving it without having the fast learn done, will it eventually learn it's self where it needs to be or should I just take it in and let them do it.  Also what exactly is the service fast learn actually doing. If I take it back I wanted to take it in and wait on it so it doesn't sit over night and cool down, as I believe the service fast learn is done in the service stall and has to be at a certain trans temp . I didn't want them brake stalling the trans to get it up to the required temp. The service fast learn is different from the individual clutch learning process.  Thanks in advance.

[Doug_Scott]

If the service bulletin had instructions for the tech to follow then it cannot be marked completed until all the steps are performed.  I wouldn't have accepted the truck back until they actually completed the job that GM paid them to do.  The manager should have had the tech perform the parts of the job that he was paid to perform without you having to make another appointment and take time out of your day to allow them to finish something they should never of let go out incomplete. 

 

That being said, I can not believe any trained tech would bring a transmission up to temp by the way you suggest.  It does not take long for the transmission to come to operating temperature.  Simply idling in gear will bring it up to temp pretty quickly provided ambient temps are over 60F.  If this fast learn is nothing more than disconnecting battery for x amount of time then reconnecting battery, having you go through the trouble of making appointment to have it done later would pissed me off to no end.

To me the fast learn sounds like it is a preset set of parameters that are closer to final auto-learn calibration than the default settings you get from disconnecting battery.  If that is correct, you are likely past that point now with the auto-learn so taking it back in will actually be a step backwards.  

[Crobinson16]

The 8l90 is a little more complicated then just disconnecting the battery to reset parameters. The service fast learn can only be done through the GDS2 and tis web as I understand it. 

As far as brake stalling the trans to bring it up to temp, gm actually list that a step in checking the trans fluid in the 8l90. I know it's ridiculous, Gus's they want to cut down on time. I don't want them doing that tie mine which is why I wanted to bring it in and have them do it then.

[Doug_Scott]

1 hour ago, Crobinson16 said:

The 8l90 is a little more complicated then just disconnecting the battery to reset parameters. The service fast learn can only be done through the GDS2 and tis web as I understand it. 

As far as brake stalling the trans to bring it up to temp, gm actually list that a step in checking the trans fluid in the 8l90. I know it's ridiculous, Gus's they want to cut down on time. I don't want them doing that 

Does your owners manual suggest you do that prior to checking fluid level if transmission is cold?  Back when I was doing transmission work(decades ago) the first thing I did was a road test.  That will warm up the fluid, and confirm that the issue I am looking for is actually what customer thought it was. I can understand running the truck with parking brake applied idling in gear with drive wheels off ground if road test is not allowed, but would be afraid of something unforeseen happening while doing what they suggest. Having a foot slip can create a good size dent in your toolbox that warranty won't pay for. 

I think what you are describing fits my thoughts on pre-loading an "enhanced" set of parameters.  GM tech line may get a copy of settings from all 8l90 transmissions and create a average initial settings that replicates what you may generate yourself halfway through a complete relearn from basic default settings.  If that's the case it would be helpful if service manager knew and told you at the time. 

[Crobinson16]

6 hours ago, Doug_Scott said:

Does your owners manual suggest you do that prior to checking fluid level if transmission is cold?  Back when I was doing transmission work(decades ago) the first thing I did was a road test.  That will warm up the fluid, and confirm that the issue I am looking for is actually what customer thought it was. I can understand running the truck with parking brake applied idling in gear with drive wheels off ground if road test is not allowed, but would be afraid of something unforeseen happening while doing what they suggest. Having a foot slip can create a good size dent in your toolbox that warranty won't pay for. 

I think what you are describing fits my thoughts on pre-loading an "enhanced" set of parameters.  GM tech line may get a copy of settings from all 8l90 transmissions and create a average initial settings that replicates what you may generate yourself halfway through a complete relearn from basic default settings.  If that's the case it would be helpful if service manager knew and told you at the time. 

Owner's manual does not tell you to check the fluid, the 8l90 has no dipstick. Take to dealer if visible fluid is leaking. Available to the public if you wish to check it your self,  the procedure from gm list the steps and temp to properly check the trans fluid. And in the list states to test drive till temp is reached , but also states that in the service bay it my be nessary to brake stalling the trans for 10 seconds at a time to reach the proper temp. However I am totally against that as you can do severe damage.  The service fast learn and individual clutch learning procedures are specific to each 8l90 platform. It may over time learn where it needs to be but I'm not 100 sure as I'm not a certified gm tech. I posted this here in this section " Ask a gm technician" with thoughts of getting a answer from a GM technician. I did talk the service manager again, and he said he missed it on the bultion. After reading it I understood how he missed it. 

[Jsdirt]

Dude ... you paid what? $50 LARGE for the truck?  TAKE IT BACK IN.

 

Make them fix it CORRECTLY,  no matter what internal issues GM has created for themselves.

Edited April 20, 2018 by Jsdirt

[Doug_Scott]

Did a quick search for 8l90 fast learn and got this as second return

http://sandyblogs.com/techlink/?p=4478

 

According to this link the fast learn has been a requirement since the 6 speed was introduced, albeit to a much lesser amount.  The 8l90 needs the fast learn done after any repair or update.  The tech should know this, and unless your truck was his first hands on repair of either the 6 speed or 8l90 it should have been second nature. 

 

The above link gives a basic description of the fast learn.  The way I understand it the fast learn is what I thought it was.  Chances are your transmission is getting better each mile you drive and by the time you get back to the dealer, having the fast learn performed will be a step backwards. I would still get it done, but would also insist it being done while you wait. Should only take 10 minutes maximum. 

 

[Crobinson16]

Took the truck back in to the dealership to have the transmission service fast learn completed after having the updated TCM calibration for improved shifting. I can say for a fact that the truck drives and shifts better after having the service fast learn done. They were infact to do the fast learn after doing the updated TCM calibration it didn't get done on Friday , but they did it for me this morning while I waited. I'm glad I took it back to have it done. Also before I took it in this morning , I looked to see if there were any ecm calibration updates. They were two showing that may be available. They hooked it up and they were so they updated the ecm calibrations as well. My fuel mileage is back to where it was prior to the TCM calibration. So either the fast learn or the ecm calibrations or a combination of the two have deffentaly made a difference in how the truck preforms. I recommend anyone to check in TIS WEB or with there dealer to see if any updates may be available. They don't cost anything if you are still under warranty. And if you are not i feel it's still beneficial for the shop rate which should only be a one hr charge.