2016 GMC Sierra 1500 CC Z71 8L90 2nd to 1st downshift issues

Silverado8SPD53 · October 3, 2016

I have experienced similar transmission problems. Here is the email that I sent to Mary Barra...

Hello Mary,

I hope that you can help me resolve an issue that I have been experiencing with my new GM Vehicle. I purchased a 2016 Silverado LTZ 5.3L - 8 Speed in February of this year. Not long after purchasing the vehicle I noticed that the truck would sometimes jerk hard/shudder just before coming to a stop. I took the truck to the dealership service department, with less than 100 miles on the vehicle and the mechanic replaced the Torque Converter. The mechanic said that it felt like driving on the “rumble strips” that are on the side of the road while breaking. In agreement with his description, I was hopeful that the issue would be resolved. Unfortunately after 4-5 attempts to fix the issue(s) by the dealership over the course of 7 months my issue has not been resolved.

The issue(s) that I am experiencing all appear to be with the trucks 8 speed transmission. The first two occur during breaking and the third happens when accelerating from a “cold” start. A description of each of the three major issues are outlined below:

1) During initial breaking the truck will begin to slow down as intended and without warning it abruptly accelerates/slides forward (See breaking profiles). This typically happens between 10-20 MPH.

2) During breaking just before coming to a stop I experience a hard jerk or shudder (See breaking profiles).

3) During a “Cold” start, in the morning or after work, the transmission will sometimes slip and shift hard while pulling out of my driveway/parking lot.

The issues are all intermittent so I document them with a Data Acquisition System. I instrumented the truck with a DC accelerometer, positioned under the driver seat to measure fore/aft acceleration, and collected data using a portable Data Acquisition System while driving. A sample of my findings are presented below:

Any assistance that you could provide in helping me resolve these issues would be greatly appreciated.

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Nick from the executive office contacted me and after 30 days of emails and phone calls I received the following response today:

Nick Wrote:

I have spoke to the DMA and CE at Mike Castrucci and was told that they road in your vehicle and road in a comparable vehicle and found that the issue you are describing are a normal characteristic of the vehilce. I know that this is the same resolution that was given to you before by this dealership, and it seems that they are sticking to it.

The only recourse we have right now is to get another opinion from a near by dealership, and it would seem that we have already done that in your area. There is not a lot for us to do that this time unfortunately.

Thank you,

Nicholas Miller

General Motors

Executive Assistant

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4emeryj44 · October 4, 2016

Well first off, to everyone who has responded and put their issues with their trucks, I feel for you and I truly hope that we can all get our vehicle issues resolved.

So today I dropped the truck off at the dealership, and hoping the Engineer would be there to drive around, of course not! I asked when he would be in, they said "Well the Engineers don't really coordinate with us and let us know when they will be in". So I left very frustrated today. My GM Executive Liason, who is now Shantiniquea Lee, was in contact with me today as well. They are building my case load, all Requisition/ticket numbers on the services/work performed tickets, and all that such stuff. She told me that the "Engineer", who by the way isn't specifically a GM Engineer, is at other dealers looking at other vehicles, we hope by Friday he can get to yours. It's all good, I figured this would happen, and I will wait patiently to seem what the disposition of the truck will be.

On a different note, I contacted a Lemon Law Lawyer here in Virginia. Got some good info so might want to pay attention for all people interested in this. So my truck fully qualifies for lemon law at this point, it has been in the shop (documented) 3 times or more for the same issue without a resolution. NOW, here's where it gets tricky, you have to "inform" the manufacturer that there is an issue and you would like to lemon law the vehicle. That can be done one of a couple ways. 1st, you can provide that in the form of a letter, they have a certain amount of time to respond. 2nd, they send a factory/field engineer out to look at the vehicle (in my case) and that is the manufacturer ACKNOWLEDGING that there is an issue for lemon law. So unfortunately the lawyer said they technically have 1 more attempt to fix if I did go the lemon law route.

So what I'm going to do, is wait patiently and professionally. When the disposition of the truck comes back and the deal that GM wants to make with me, that will determine what I will do. So at first I was mentally going to be okay with getting a similar truck, I mean what are the chances it would happen again. But I actually do know personally a few people (not just online) that have major issues with their 2015 and 2016 8 speed transmissions. I honestly do NOT want another truck with the 8 speed, I don't trust it, and I definitely DO NOT want to go through this process again. I'm so done going to the dealer and getting a rental SUV that I don't care to drive, I want my nice big comfortable 4WD truck. So I truly want to find a used truck, but from what I've heard they wont allow you to do that, they want you to rebuy a new truck.

Anyways, I could go on for hours. Those are the facts as it stands right now, they are building the case, truck will get driven and looked at and either fixed or they will give me another truck or buy me out or i'll lemon law. So if anyone has an questions or anything along those lines feel free to post or message or even give me a call. I'd be glad to share any and all information I have. Good luck to everyone.

Silverado8SPD53 · October 4, 2016

Did you file a complaint at safercar.gov?

https://www-odi.nhtsa.dot.gov/VehicleComplaint/

4emeryj44 · October 4, 2016

Did you file a complaint at safercar.gov?

https://www-odi.nhtsa.dot.gov/VehicleComplaint/

I have not done that, what will that accomplish? I mean I'm all for making a complaint just honestly don't know what that will do or who it will benefit? Let me know.

mookdoc6 · October 5, 2016

I honestly can't see you having the same luck with another 8speed? Who knows though I have had pretty shitty luck too at times......Good Luck!

Rwrows · October 9, 2016

I have a 16 Denali 6.2 a8. My truck has does this once in a while but I believe it's the driver. Like when I get sloppy and I tap the gas just to slam on the brakes for a stop sign the trans will act goofy sometimes. But if I drive the truck carefully it's fine. I think they all do it. Just some guys drive differently and come across it more. It's seems the truck doesn't like it when the driver wastes gas. I drove another of the same truck before I bought mine. I felt the hard 1-2 shift pulling out but chalked it up to the truck sitting on the dealer lot for a while. Overall my truck has been pretty darn good. Once I felt the trans bang so hard that I found it embarrassing. But again that was when I tapped the gas and hit the brakes immediately after. The driver has a lot to do with it. I had a 16 ram rental and that a8 seemed pretty flawless. Hard for me to own a dodge though.

Dnt · October 10, 2016

I have a 16 Denali 6.2 a8. My truck has does this once in a while but I believe it's the driver. Like when I get sloppy and I tap the gas just to slam on the brakes for a stop sign the trans will act goofy sometimes. But if I drive the truck carefully it's fine. I think they all do it. Just some guys drive differently and come across it more. It's seems the truck doesn't like it when the driver wastes gas. I drove another of the same truck before I bought mine. I felt the hard 1-2 shift pulling out but chalked it up to the truck sitting on the dealer lot for a while. Overall my truck has been pretty darn good. Once I felt the trans bang so hard that I found it embarrassing. But again that was when I tapped the gas and hit the brakes immediately after. The driver has a lot to do with it. I had a 16 ram rental and that a8 seemed pretty flawless. Hard for me to own a dodge though.

I was curious so tried that maneuver hit the gas at slow speeds then immediately hit the brakes. I got a harsh 2nd to 1st shift. It has never in 7000 miles of driving done that before. Not too awful bad but very noticeable. I may have to trade it in now....

4emeryj44 · October 10, 2016

So the engineer came back and is "very confident that they know what is wrong with the truck." They are going to replace the TCM and do the adaptive relearn procedures. By the way this has already been done, now granted that was before they replaced the transmission, so the new tranny has the old TCm in it. I highly doubt this will fix it. I called and left a voicemail along with an email basically stating that if they "fix" the truck and give it back to me and it's not perfect or it doesn't fix it I will immediately lemon law the truck and I have a lawyer waiting for my phone call. I am very surprised that gm is willing to put a customer through this many fixes and not buy the truck back to get me in a product that performs correctly. I am very disappointed by this and now will second guess buying another GM product. Which I believe that if they would have taken care of me with a buyback at this point that would have stayed loyal as I have been to gm for most of my life.

mookdoc6 · October 10, 2016

You seem very confident that it will not fix your problem? Why not see what happens and than if your not satisfied get you a Ferd after that? I get it your pissed just see what transpires. Keep us posted!

Somebody posted problems with tranny and they did the relearn and it worked for him?

jetfixer737 · October 12, 2016

I'm interested in what a new TCM will do as well. I tend to agree it won't give a satisfactory fix. From all that I've read & researched, (just my own opinion) I just don't think the transmissions are bad, nor the torque converters (Other than certain isolated faults) nor do I think the TCM is bad. Personally, I really believe its the installed computer software that controls the transmission. And in this one particular area, I don't believe GM is doing any investigating, or troubleshooting whatsoever. For example I read here somewhere about a gentleman who had a brand new transmission installed and it made absolutely no difference. So unless they all have the same mechanical defect somewhere inside, (Which I just can't believe) the problem must exist elsewhere...

Or I'm completely wrong.

mookdoc6 · October 12, 2016

I'm interested in what a new TCM will do as well. I tend to agree it won't give a satisfactory fix. From all that I've read & researched, (just my own opinion) I just don't think the transmissions are bad, nor the torque converters (Other than certain isolated faults) nor do I think the TCM is bad. Personally, I really believe its the installed computer software that controls the transmission. And in this one particular area, I don't believe GM is doing any investigating, or troubleshooting whatsoever. For example I read here somewhere about a gentleman who had a brand new transmission installed and it made absolutely no difference. So unless they all have the same mechanical defect somewhere inside, (Which I just can't believe) the problem must exist elsewhere...

Or I'm completely wrong.

I would have to lean in the direction of software too! I mean there is much going on with Software/Trans/Engine? Anyway, I had dealer look into the the dreaded first shift in the morning being a clunk and subsequent random 1-2, 2-1 downshifts that didn't feel correct which was hit and miss. I got phone message stating the Tech took it for lengthy road test and found some "bumps" Anyway, they Fast learned the C4 Clutch pads/packs? For a softening is all it stated! Tech told the service advisor that truck is synced and dialed in perfect!

Driving in now is completely different! I always stated the 3-8 I honestly could not really feel when it shifted but always had this pedal feel in 1-2, 2-1 area! Now, I can't feel anything! So, going back to your statement yup I would agree 100% it's all software related!

MOhunter92 · October 12, 2016

I'm interested in what a new TCM will do as well. I tend to agree it won't give a satisfactory fix. From all that I've read & researched, (just my own opinion) I just don't think the transmissions are bad, nor the torque converters (Other than certain isolated faults) nor do I think the TCM is bad. Personally, I really believe its the installed computer software that controls the transmission. And in this one particular area, I don't believe GM is doing any investigating, or troubleshooting whatsoever. For example I read here somewhere about a gentleman who had a brand new transmission installed and it made absolutely no difference. So unless they all have the same mechanical defect somewhere inside, (Which I just can't believe) the problem must exist elsewhere...

Or I'm completely wrong.

It's for sure software related. Press in your tow mode button on your shifter and hold for 5 seconds and release. You will notice your shifts will clean up, pretty significantly. I think the tune is bad for the 8 speed, it down shifts too late from 2-1. If it was a quicker and earlier downshift, that would solve the problem. With grade braking off, it cleans up considerably.

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mookdoc6 · October 12, 2016

I had Zero difference with grade brake off. I thought at first it was better but it was just Placebo "effect" 4emery44J probably had a junk torque converter 1st time and probably many others still a small percentage. The rest just have software issues "programming" etc. Which is why they will have multiple Flashes over the production run of these 5.3L to 8speed combos!

4emeryj44 · October 12, 2016

So just another update real quick.

Dealer called me yesterday and said "Well sir we made GREAT STRIDES and your truck is definitely better, BUUUTTTT, we want your consent to have the technician drive it back and forth to work for a week so that we can make sure the relearn cleans things up and tune the truck more if need be."

So what that tells me is that replacing the TCM didn't quite get the results they wanted and now they are trying to let the technician drive it and put some miles on it because they know if they would give me the truck now I'd just lemon law it. So I don't think the driving is going to resolve anything but whatever. At this point, I want to so badly lemon law the truck on the first inclination of there being hard shifting because I know damn well it's still going to be there, but I don't know if I have it in me anymore to fight this. I think honestly I'm going to accept the truck back, and just go to a different dealer and trade the damn thing in. Sucks because I invested in a really expensive extended warranty that ill lose but at this point I fear the truck will never be right, I hate the 8 speed, and I'm going to buy an older Silverado/sierra with the 6 speed and get a new truck in a few years when all these crazy high speed transmissions get worked out.

I'm interested in what a new TCM will do as well. I tend to agree it won't give a satisfactory fix. From all that I've read & researched, (just my own opinion) I just don't think the transmissions are bad, nor the torque converters (Other than certain isolated faults) nor do I think the TCM is bad. Personally, I really believe its the installed computer software that controls the transmission. And in this one particular area, I don't believe GM is doing any investigating, or troubleshooting whatsoever. For example I read here somewhere about a gentleman who had a brand new transmission installed and it made absolutely no difference. So unless they all have the same mechanical defect somewhere inside, (Which I just can't believe) the problem must exist elsewhere...

Or I'm completely wrong.

With my truck, putting it into tow/haul or turning off grade braking helped but still wasn't a complete fix, which does tell me that it is a lot to do with software I think. You would think that they would take more interest in this because I know a few people that have the 8 speeds and it does the same thing mine originally did and they just deal with it and don't take the truck in. They have more issues with these 8 speeds or tuning than GM realizes. And this is a brand new transmission like 3k miles ago, truck only had 15,000 miles when it was replaced and still clunking and crazy shitty shifting persisted.

It's for sure software related. Press in your tow mode button on your shifter and hold for 5 seconds and release. You will notice your shifts will clean up, pretty significantly. I think the tune is bad for the 8 speed, it down shifts too late from 2-1. If it was a quicker and earlier downshift, that would solve the problem. With grade braking off, it cleans up considerably.

Sent from my iPhone using Tapatalk

I agree with the software related issues, but sometimes I question it because no matter what TCM or tuning they do it still never fully fixes it. And I COMPLETELY agree that it downshifts WAAAAYYYY too late from 2-1. I'm driving a 2017 GMC Yukon as a loaner and it has the 6 speed and it's a COMPLETELY different acting truck and transmission. the shifts are predictable and what you would feel from a truck. Like I have to give it gas for it do shift from 1st to 2nd, my 8 speed I barely touch throttle just to move up one car length and it shifts to 2nd. I hate it!!!!!!

mookdoc6 · October 12, 2016

When all these crazy high speed transmissions get worked out? I drove first factory GM trucks with 6speed when they first came out! They sucked awful and needed multiple software rewrites. Now, this 6speed is in the end of it's run and is 100% better and that would be natural course of action. It will be just the same for the 8speed probably! I had a early run Malibu with 6speed and needed countless tranny flashes. I feel for ya brother the software is killing us!