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

4emeryj44 · May 24, 2016

So I know this is like a damn dead horse being beaten, but I more or less want to post my experience with my truck just to throw it out there. To start, I bought my truck around Christmas time in Tennessee, love the truck. Approximately at around 4,000 miles after the "learn" process had worn off of the truck, it started this horrible clunking, downshift from 2nd gear to 1st when coming to a stop. At first it was random, couldn't seem to figure it out or duplicate it. I went on here and had seen a lot of similar posts, mostly were the 2015's with, and supposedly the 2016's had an update and were supposedly "fixed" from what I read. Anyways, I let it go one for a few months to see if the transmission just needed to be broken in some more, at this point I had around 8,000 or 9,000 miles on it.

I ended up talking with a GM technical support person from here and they set me up with a case number and to get in contact with a dealer. I end up going to the dealership for this issues, a second oil change and tire rotation for an upcoming move to Virginia in which I was going to haul a trailer with my house hold goods. So I wasn't able to duplicate it of course!!! classic. But the transmission technician did notice it being kind of clunky and sloppy, so he put it back into re-learn mode. After driving it, it seemed a little better so I went with it. I had talked to a friend of mine who bought the EXACT same truck as me, same transmission, rear end, motor, everything except the color from the same dealer about a month after I did. He said he experienced some similar issues I was having, but then he had towed a trailer from Tennessee to Arizona, then after that truck shifted like a dream. So of course I say to myself "i'll wait till I tow then if the problem persists i'll take it to a dealer". So I'm now in Virginia, truck towed PHENOMINAL, wasn't the heaviest of trailers, but had about 2,500 pounds of furniture and fuel and cargo and trailer, so a decent amount. Boy did GM do a great job with building the transmission and tuning on the computer for towing, I was very impressed.

So then I drop the trailer off, into a temporary house at the moment, and the truck is back to it's old ways of this horrible downshift. It feels like I'm being rear-ended, and I fear that I could potentially hit the car in front of me at times, it's that bad. So I narrowed it down to the exact situation in when it does this. So say you start out in 1st gear (obviously) and you slowly hit the gas JUST ENOUGH to shift into second as if you were creeping up to a stop sign, it shifts to 2nd, then you want to come to a stop, BAM! huge jolt, huge clunk, again feels like I got rear ended. But if you take off from a light, get up to say 30 MPH go through a majority of the gears and then come to a stop, not a problem at all. Also, in tow/haul mode while towing, no issues at ALL, smooth as butter.

So this leads me to believe that it has to be computer related, but honestly I'm not sure. I'm going to the new dealership tomorrow, and I just wanted to share my experience thus far.

redwngr · May 24, 2016

Try disabling 'normal mode grade braking' after startup for a few days and see if you can detect a difference.

(hold the tow haul button depressed for more than 5 seconds and then release. The dic should give a message that grade braking is disabled)

4emeryj44 · May 24, 2016

Try disabling 'normal mode grade braking' after startup for a few days and see if you can detect a difference.

(hold the tow haul button depressed for more than 5 seconds and then release. The dic should give a message that grade braking is disabled)

I did try that last night and drove it around the block, didn't seem to do much good, again it was only 1 drive and not a few days. Took it into the local dealership here and took the transmission tech and drove him around. He said "wow that's bad", so he said he is going to immediately call higher up and see if there are any like known issues, then dive into the issue. He and I both think it's the computer settings, I know there is no update right now, but again I think somehow the settings either in the TCM or whatever have to be off, or need recalibrated somehow.

SierraMyst · May 24, 2016

So I know this is like a damn dead horse being beaten, but I more or less want to post my experience with my truck just to throw it out there. To start, I bought my truck around Christmas time in Tennessee, love the truck. Approximately at around 4,000 miles after the "learn" process had worn off of the truck, it started this horrible clunking, downshift from 2nd gear to 1st when coming to a stop. At first it was random, couldn't seem to figure it out or duplicate it. I went on here and had seen a lot of similar posts, mostly were the 2015's with, and supposedly the 2016's had an update and were supposedly "fixed" from what I read. Anyways, I let it go one for a few months to see if the transmission just needed to be broken in some more, at this point I had around 8,000 or 9,000 miles on it.

I ended up talking with a GM technical support person from here and they set me up with a case number and to get in contact with a dealer. I end up going to the dealership for this issues, a second oil change and tire rotation for an upcoming move to Virginia in which I was going to haul a trailer with my house hold goods. So I wasn't able to duplicate it of course!!! classic. But the transmission technician did notice it being kind of clunky and sloppy, so he put it back into re-learn mode. After driving it, it seemed a little better so I went with it. I had talked to a friend of mine who bought the EXACT same truck as me, same transmission, rear end, motor, everything except the color from the same dealer about a month after I did. He said he experienced some similar issues I was having, but then he had towed a trailer from Tennessee to Arizona, then after that truck shifted like a dream. So of course I say to myself "i'll wait till I tow then if the problem persists i'll take it to a dealer". So I'm now in Virginia, truck towed PHENOMINAL, wasn't the heaviest of trailers, but had about 2,500 pounds of furniture and fuel and cargo and trailer, so a decent amount. Boy did GM do a great job with building the transmission and tuning on the computer for towing, I was very impressed.

So then I drop the trailer off, into a temporary house at the moment, and the truck is back to it's old ways of this horrible downshift. It feels like I'm being rear-ended, and I fear that I could potentially hit the car in front of me at times, it's that bad. So I narrowed it down to the exact situation in when it does this. So say you start out in 1st gear (obviously) and you slowly hit the gas JUST ENOUGH to shift into second as if you were creeping up to a stop sign, it shifts to 2nd, then you want to come to a stop, BAM! huge jolt, huge clunk, again feels like I got rear ended. But if you take off from a light, get up to say 30 MPH go through a majority of the gears and then come to a stop, not a problem at all. Also, in tow/haul mode while towing, no issues at ALL, smooth as butter.

So this leads me to believe that it has to be computer related, but honestly I'm not sure. I'm going to the new dealership tomorrow, and I just wanted to share my experience thus far.

My truck (2016) and many others do the same thing.

Dealers all say it normal. Never felt it in any other vehicle I've owned. I have three vehicles now, one 7 speed and two 8 speeds (including the Sierra). Only the Sierra does this nonsense.

I can't believe they produced this piss poor performing transmission. And their only answer for it is "it's normal".

I am certain you are right. It's all programming of the TCM and it's shift points. During normal driving the truck shifts to 2nd gear at 10 mph. 3rd by 18, 4th at 25, and 5th at 39.

Those are insane shift points specifically designed with gas mileage in mind for the general consumer.

(G)overnment (M)otors has only one customer's vested interest, and that's the federal government and their EPA standards.

You know what's really going to get your goat...this shift point programming already exist. My employer (a federal agency) uses nothing but GM vehicles. We have many-many suburbans, yukons, cadicallacs, and silverados. Many of them transport important individuals. You know how many of them clunk and slam into gear, & shutter.....NONE. They know the hand that feeds them.

Sadly, after a long life of owning Toyotas and Nissans, I made the mistake of buying a GM based on the cars and trucks I drive at work.

Unfortunately, they are not the same vehicle.

I love the truck, but the inconsistent abrupt shifting and clunking and shutter needs to be fixed, regardless of CAFE regulations.

What dealer in VA are you working with?

4emeryj44 · May 24, 2016

My truck (2016) and many others do the same thing.

Dealers all say it normal. Never felt it in any other vehicle I've owned. I have three vehicles now, one 7 speed and two 8 speeds (including the Sierra). Only the Sierra does this nonsense.

I can't believe they produced this piss poor performing transmission. And their only answer for it is "it's normal".

I am certain you are right. It's all programming of the TCM and it's shift points. During normal driving the truck shifts to 2nd gear at 10 mph. 3rd by 18, 4th at 25, and 5th at 39.

What dealer in VA are you working with?

Yeah I definitely am certain at this point it's the tuning of it. If I could program it without voiding my warranty I would. I am working with Suttle GMC in Newport News. It's funny that it's a known problem, but yet not every truck does it. My buddy has the exact same truck and it doesn't do it. So it's gotta be something.

mookdoc6 · May 24, 2016

^{When is your build date? The Torque converter is new after Jan of Feb 2016 I read in one of these fourms........}

4emeryj44 · May 25, 2016

^{When is your build date? The Torque converter is new after Jan of Feb 2016 I read in one of these fourms........}

I have heard some issues with torque converters, where would I find my trucks build date? I bought the truck in December of 2015 if that says anything about the date.

GMCustomerService · May 25, 2016

I did try that last night and drove it around the block, didn't seem to do much good, again it was only 1 drive and not a few days. Took it into the local dealership here and took the transmission tech and drove him around. He said "wow that's bad", so he said he is going to immediately call higher up and see if there are any like known issues, then dive into the issue. He and I both think it's the computer settings, I know there is no update right now, but again I think somehow the settings either in the TCM or whatever have to be off, or need recalibrated somehow.

Hello 4emeryj44,

I apologize for the rough shifting in your Sierra and understand your frustrations with experiencing concerns in a new vehicle. I would be happy to review your current case in greater detail. If you could private message me your VIN or case number I can research this on my end to see if there is any new information available for you.

Have a good day.

Julianne M.

GM Customer Care

UWMad · May 25, 2016

So I know this is like a damn dead horse being beaten, but I more or less want to post my experience with my truck just to throw it out there. To start, I bought my truck around Christmas time in Tennessee, love the truck. Approximately at around 4,000 miles after the "learn" process had worn off of the truck, it started this horrible clunking, downshift from 2nd gear to 1st when coming to a stop. At first it was random, couldn't seem to figure it out or duplicate it. I went on here and had seen a lot of similar posts, mostly were the 2015's with, and supposedly the 2016's had an update and were supposedly "fixed" from what I read. Anyways, I let it go one for a few months to see if the transmission just needed to be broken in some more, at this point I had around 8,000 or 9,000 miles on it.

I ended up talking with a GM technical support person from here and they set me up with a case number and to get in contact with a dealer. I end up going to the dealership for this issues, a second oil change and tire rotation for an upcoming move to Virginia in which I was going to haul a trailer with my house hold goods. So I wasn't able to duplicate it of course!!! classic. But the transmission technician did notice it being kind of clunky and sloppy, so he put it back into re-learn mode. After driving it, it seemed a little better so I went with it. I had talked to a friend of mine who bought the EXACT same truck as me, same transmission, rear end, motor, everything except the color from the same dealer about a month after I did. He said he experienced some similar issues I was having, but then he had towed a trailer from Tennessee to Arizona, then after that truck shifted like a dream. So of course I say to myself "i'll wait till I tow then if the problem persists i'll take it to a dealer". So I'm now in Virginia, truck towed PHENOMINAL, wasn't the heaviest of trailers, but had about 2,500 pounds of furniture and fuel and cargo and trailer, so a decent amount. Boy did GM do a great job with building the transmission and tuning on the computer for towing, I was very impressed.

So then I drop the trailer off, into a temporary house at the moment, and the truck is back to it's old ways of this horrible downshift. It feels like I'm being rear-ended, and I fear that I could potentially hit the car in front of me at times, it's that bad. So I narrowed it down to the exact situation in when it does this. So say you start out in 1st gear (obviously) and you slowly hit the gas JUST ENOUGH to shift into second as if you were creeping up to a stop sign, it shifts to 2nd, then you want to come to a stop, BAM! huge jolt, huge clunk, again feels like I got rear ended. But if you take off from a light, get up to say 30 MPH go through a majority of the gears and then come to a stop, not a problem at all. Also, in tow/haul mode while towing, no issues at ALL, smooth as butter.

So this leads me to believe that it has to be computer related, but honestly I'm not sure. I'm going to the new dealership tomorrow, and I just wanted to share my experience thus far.

You couldn't have wrote this any better! My new 2016 Z71 LTZ with the 8-speed does the exact same thing. There's been multiple times where is jerked forward so hard...thank god I had my foot on the brake or I would have hit the car in front of me. Starting to really miss my Dodge Ram I turned in for this one...except for one thing...the gas mileage! I do get better mpg with this one vs the Ram...and it's noticeable.

4emeryj44 · May 26, 2016

Well I received my truck back from the dealer today, and I definitely have some news on the work that they performed, but pretty much what I get out of it is they are "tuning" the transmission on the individual clutch for the 2-1 gear shift and trying to soften it up. I will go into more details tomorrow being that it's late. I haven't driven it around TOO much, but from what I can tell so far it seems better that's for sure.

4emeryj44 · May 26, 2016

***UPDATE***

Alright, so to hit on what the dealership did for a bit, then i'll go into how the truck is doing so far. So the technician called Technical Assistance for guidance since previously a "relearn" didn't fix anything. The guidance was to apply the #16-NA-019 "bulletin" I guess you'd call it. Title is "Information on Transmission Adaptive Functions and Correcting Low Mileage Harsh Shifts, Slips, or Flares - (Jan 25, 2016). Basically to briefly describe what it entails, is due to tight tolerances on low mileage vehicles with this transmission, they sometimes will have to adjust or "tune" the individual Clutch Pack that controls that specific gear shift, so my issue was the 2nd gear to 1st gear shift at very low speed, the table in the bulletin shows the C3 clutch being the applying clutch, and the C4 clutch the releasing clutch. So they used a program called "Transmission Service Fast Learn". Basically what the technician does is adjust that specific clutch, then drives it, notes whether its better or worse, or requires more adjusting, then re calibrates until desired results are achieved. So that is what was done to my truck.

Results: So I drove the truck this morning running errands, and noticed a considerable improvement with the shifting. I'm assuming its still kind of in a relearn mode with the adjustments that were made, but definitely better than it was when I took the truck in. I truly believed from the beginning of all of this that it was in the tuning of the TCM or something to that affect. In the bulletin previously mentioned, it does an overview which I believe to have been true with what GM did with this. They basically gave the TCM and the transmission "adaptive learning" abilities, but it was a generalized tune and ability if you will. They knew that not all transmissions coming off the assembly line were going to be equal and would have tighter or looser tolerances that others. So, in my case, the transmission was great other than the 1-2-1 downshift at very low speeds. So that gave the techs a program that enabled them to make adjustments and "small tune calibrations" to individual clutches, so in other words you can adjust and fine tune a certain shift without messing with the rest of the shifts in the other gears.

So now I believe, with my truck that is, that this whole issue is in the tuning of it. Now whether or not i'll have to go back to get more adjustments I'm not sure, need to drive the truck more. But I feel that there is enough tuning and tweaking available that they can do to get the transmission to calm down and shift correctly. Also, I believe my transmission is built a little more "tight" than some others, and that's why I was having the issue, so they had to soften up that specific clutch with less line pressure by adjusting that specific solenoid.

Anyways, enough of me rambling, I believe anyone reading this gets the jist of what is going on here. If you have any questions please post or PM me. I want this info out there for others so they don't have to do as much research or maybe it will put them at ease a bit more.

SierraMyst · May 26, 2016

Wow. Thanks for the update.

Good to know that there's a TSB for this.

I'll be taking it in for the first oil change and mentioning this.

InertiaFaze · May 27, 2016

***UPDATE***

Alright, so to hit on what the dealership did for a bit, then i'll go into how the truck is doing so far. So the technician called Technical Assistance for guidance since previously a "relearn" didn't fix anything. The guidance was to apply the #16-NA-019 "bulletin" I guess you'd call it. Title is "Information on Transmission Adaptive Functions and Correcting Low Mileage Harsh Shifts, Slips, or Flares - (Jan 25, 2016). Basically to briefly describe what it entails, is due to tight tolerances on low mileage vehicles with this transmission, they sometimes will have to adjust or "tune" the individual Clutch Pack that controls that specific gear shift, so my issue was the 2nd gear to 1st gear shift at very low speed, the table in the bulletin shows the C3 clutch being the applying clutch, and the C4 clutch the releasing clutch. So they used a program called "Transmission Service Fast Learn". Basically what the technician does is adjust that specific clutch, then drives it, notes whether its better or worse, or requires more adjusting, then re calibrates until desired results are achieved. So that is what was done to my truck.

Results: So I drove the truck this morning running errands, and noticed a considerable improvement with the shifting. I'm assuming its still kind of in a relearn mode with the adjustments that were made, but definitely better than it was when I took the truck in. I truly believed from the beginning of all of this that it was in the tuning of the TCM or something to that affect. In the bulletin previously mentioned, it does an overview which I believe to have been true with what GM did with this. They basically gave the TCM and the transmission "adaptive learning" abilities, but it was a generalized tune and ability if you will. They knew that not all transmissions coming off the assembly line were going to be equal and would have tighter or looser tolerances that others. So, in my case, the transmission was great other than the 1-2-1 downshift at very low speeds. So that gave the techs a program that enabled them to make adjustments and "small tune calibrations" to individual clutches, so in other words you can adjust and fine tune a certain shift without messing with the rest of the shifts in the other gears.

So now I believe, with my truck that is, that this whole issue is in the tuning of it. Now whether or not i'll have to go back to get more adjustments I'm not sure, need to drive the truck more. But I feel that there is enough tuning and tweaking available that they can do to get the transmission to calm down and shift correctly. Also, I believe my transmission is built a little more "tight" than some others, and that's why I was having the issue, so they had to soften up that specific clutch with less line pressure by adjusting that specific solenoid.

Anyways, enough of me rambling, I believe anyone reading this gets the jist of what is going on here. If you have any questions please post or PM me. I want this info out there for others so they don't have to do as much research or maybe it will put them at ease a bit more.

4emeryj44,

Good to know things are going better with your truck.

A lot of what you included in your post was on the money. For example not all transmissions have exactly the same dimensional characteristics. That's the reason the TCM has the ability to measure certain parameters and make adjustments so that it achieves optimal shift quality. These adjustments occur whether Service Fast Learn is performed or not. Service Fast Learn is a procedure performed by a technician but the technician him/her self doesn't determine the adjustments, the SW does all the work. After Service Fast Learn is completed the TCM continues to measure and adjust many parameters periodically throughout the life of the vehicle. Think of it like this, the base calibration provides a generic starting point, Service Fast Learn provides an optimized starting point, and the adapts that occur while driving provide further refinements.

When Service Fast Learn is run it can't be run on a specific clutch, it runs on all of the clutches. The thing that can be performed on an individual clutch is the accelerated Drive Learn procedure. There's a TSB on that too, it's been posted here on GMT several times. It basically describes how to accelerate the adapt process that would otherwise occur through normal driving, but by purposely driving in certain conditions it greatly speeds up the adapt process. Remember also, that the TCM continues to learn throughout the life of the trans/vehicle.

Best wishes with your truck.

Skytrekin · May 29, 2016

Thank you for all of this info, I have purchased this same truck and have about 700 miles on it. I have followed the break in by keeping it under 55 mph (mostly) and haven't really noticed any harsh shifting up or down. But I am happy to read with some miles on it this is possible, and their is a fix for it.

I am amazed at all the technology these trucks have in them now. This is my first new truck in about 15 years. I love the styling of the GMC vs Chevy. I am happy with all the tech gadgets and comforts, but still remains a truck.

elcamino · May 29, 2016

I have heard some issues with torque converters, where would I find my trucks build date? I bought the truck in December of 2015 if that says anything about the date.

On the lower portion of the "B" pillar just above rocker panel is a silver label, build month and year on the top right, e.g. 05/15