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2017 ATS 3.6 Performance Premium
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Discussion Starter #1
This week I took my 2017 ATS 3.6 Premium Performance to the dealer for its regular service and asked them to investigate a transmission shudder. I have been having the typical "rumble strip" sensation upon light acceleration at moderate speed (20-45 mph) intermittently but fairly consistently most of the summer. I did notice it happens more often on warm days, and the day of my service was unseasonably cool. They called late in the day to say they could not duplicate it. My service advisor is very good and was aware of the bulletin, and told me when she broke the news and saw my dismay that I should bring it back the next time it does it and let her or her boss ride with me while I duplicated it, which I thought was reasonable. Today (a Saturday when they are not open for service) was a warm day and I could make it do it almost at will.Hopefully we get some warm days next week so I can demonstrate it for them. Since the car only has a bit more than 6000 miles on it I want this fixed ASAP and am hoping the new fluid outlined in the bulletin will do that.
 

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2014 ATS 3.6 Premium RWD, 2016 Corvette Z06, 2018 GMC Sierra Denali 2500HD Diesel
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Greg,

Your dealer needs to get with the program because the latest bulletin (August 2019) specifically states that for vehicles within the concern build period NO diagnosis is necessary beyond the customer complaint. But be sure that this really is a good dealer using the correct fluid because this is a one time only flush with the latest bulletin and anything beyond that will require full diagnostics; some dealers have used previous revisions of this fluid which isn't surprising because there have been so many.

See attached PDF and highlight the no diagnostics part for your dealer.

Rodger
 

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Mercedes C300 Luxury - ATS retired (torque coverter shudder)
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Yes, as always rsingl is spot on.

All dealerships, indeed all of GM, is painfully aware of the problem, each dealership has dealt with hundreds, if not thousands, of these tourque converter shudder cases.

For crying out loud they have a major class action lawsuit against them for exactly this widespread issue. Making you come back is ludicrous.

Unfortunately, they only will put a bandaid on the problem if you do get approval. Fluid excanges only mask the underlying issue. GM has NO FIX for this problem, hence the lawsuit.

I sold my ATS (that I otherwise LOVED) for exactly this shudder problem.
 

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Discussion Starter #4
Thanks for that Rodger. Trust me, they will end up doing this.
 

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2018 ATS Sedan Turbo AWD (stablemates 2019 Corvette Stingray + 2010 LaCrosse CXS)
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Greg,

Your dealer needs to get with the program because the latest bulletin (August 2019) specifically states that for vehicles within the concern build period NO diagnosis is necessary beyond the customer complaint. But be sure that this really is a good dealer using the correct fluid because this is a one time only flush with the latest bulletin and anything beyond that will require full diagnostics; some dealers have used previous revisions of this fluid which isn't surprising because there have been so many.

See attached PDF and highlight the no diagnostics part for your dealer.

Rodger
If I am reading this correctly then any ATS manufactured before Feb.1/19 qualifies?
 

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If I am reading this correctly then any ATS manufactured before Feb.1/19 qualifies?
Correct, that was the break point when the current fluid was in place for most product lines with a month later for others based upon the supply chain.

The current explanation is the older fluid versions were excessively hygroscopic which made some sense for the Corvette platform where the transmission coolers are only of the air to fluid type and in light duty operation the transmission fluid stays cool enough that moisture isn't driven off. But most 8Lxx applications use either a transmission to engine coolant heat exchanger or the coolant heat exchanger plus an additional air to fluid cooler in heavier applications and for those 8Lxx equipped vehicles the transmission fluid will absorb heat from the engine coolant which is usually going to be in the 150 to 160F range on the cooled tank side of the radiator raising the transmission fluid to a reasonable operating temperature even in "grandma" type driving. And if the fluid itself was the only issue, shudder should have also shown up in the 2014 Corvette C7 which has the same transmission cooler setup but the older 6Lxx transmission. There is clearly a design flaw in the 8Lxx family of transmissions.

Rodger
 

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There is some type of manual procedure for the trans to relearn shift points, but I can't find it.
 

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There is some type of manual procedure for the trans to relearn shift points, but I can't find it.
Art, these are learning/adaptive transmissions and actual shift performance is compared to desired shift performance and when there is a deviation then adjustments are made including clutch pack apply/release timing and force. In general the programming is designed to compensate over the life of the transmission for clutch pack wear and for this they use a slow learning/adapt process where only minor changes are made to compensate over time. But they are "born" with the controller in fast adapt mode which allows the transmission to quickly learn proper shifting but the program then transitions to slow mode. The dealer can reset the controller into fast adapt mode to cure some shift performance problems and for best results the problematic shift is exercised multiple times right after the reset. The magic of these transmissions is precision control of multiple clutch packs where ranges are selected by extremely precise timing of applying and releasing different clutch packs with near zero slippage and perfect timing that assures that two ranges are not commanded simultaneously even for an instant. This type of system wasn't practical until very fast and capable controllers were married with high precision measurement of the various transmission shaft speeds and prior to that we had "dumb" automatics that relied upon far less precise mechanical controls and designed in slippage to make up for the lack of precision during shifts which could otherwise result in having parts blow out the side of the case.

If a properly operating transmission suddenly develops a severe shifting issue, then I would avoid a reset to fast adapt mode because there is probably an underlying problem (failing force solenoid, damaged clutch pack, etc.) which at most will be slightly and temporarily masked by the forced fast learn process. Putting a transmission back into fast learn mode is most appropriate when hard parts are changed so that it can adapt to the new components or when early in life it has learned bad habits often due to the driving environment. My first experience with one of the higher tech clutch to clutch adaptive learning transmissions was in my 2001 GMC Sierra and the Allison transmission controller had multiple memory cells, called "taps" by Allison, for each shift based upon operating conditions and they were very specific. At 4, 000 miles I had mine put back into fast adapt mode because of a poorly executed 3 to 4 upshift that only occurred within a specific light/moderate throttle range on a slight grade and with the AC compressor active. Within 200 miles after fast learn was re-enabled that problem disappeared forever. I sold that diesel pickup to a colleague when I bought a crew cab in 2006 and his son is still driving it with over 350,000 miles on it now and all that the Allison has ever had done was I replaced the shallow GM pan with the standard Allison deep pan and matching filter, a few fluid changes, and a lot of spin on external filter changes. The son had been taking it to a few diesel truck drag races but his dad finally convinced him that "Stormy" (so named because the GM paint name for it was storm gray and it was born in and held up in production for several days due to a severe blizzard) is getting a bit up in years for kid games.

Rodger
 

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Discussion Starter #9
Today was a much warmer day than the day last week when the ATS was in for service and once again I was able to duplicate the shudder pretty much at will. I decided to take the service writer's offer of taking her out for a drive when it was doing it so she could attest to the condition with the techs, so I swung by the dealer. I also had a copy of bulletin 18-NA355 in hand.

I described that it was doing it again and also gave them page 1 of the bulletin. Neither she nor her boss had ever seen it before. After confirming the bulletin was legit, her boss then started trying to explain that it did not say what I read it as saying (i.e. if the customer says it is shuddering, do the flush and replace with the new fluid) and claimed it only applied to vehicles in dealer inventory. He said they would still need to do the full Picoscope routine for GM to pay the warranty claim. He also went on about how perhaps it could be another problem and if they didn't do the full diagnostic routine it wouldn't be found or fixed (of course, that was why it was there for a full day last week, but whatever). Bottom line, he would not guarantee the fluid flush and change would be done. I told him I did not want to waste another day only to have it come back as "Could not duplicate" again. We got into it a bit, not nastily, but I assured him that if it wasn't done the issue would be escalated and that he should confirm his interpretation with others higher up the food chain. I felt bad for the service writer because it seemed clear she read it the way I did and wanted to just get the service done. In any event, it is going back in Thursday. Could be interesting.
 

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Call GM Canada in Oakville, Ontario and complain specifically about the issue AND your local Nova Scotia dealership's unwillingness to resolve the problem as per GM's own documentation.
I wondered if the 8L45/LGX combination had the same shudder issue because each case I'd read about here seemed to be the 8L45 mated to the turbo 4. I have the LFX/6L45 setup, and I'll take the 3-4% in added fuel consumption over having to deal with this GM fumble.
 

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Call GM Canada in Oakville, Ontario and complain specifically about the issue AND your local Nova Scotia dealership's unwillingness to resolve the problem as per GM's own documentation.
I wondered if the 8L45/LGX combination had the same shudder issue because each case I'd read about here seemed to be the 8L45 mated to the turbo 4. I have the LFX/6L45 setup, and I'll take the 3-4% in added fuel consumption over having to deal with this GM fumble.
The lawsuit names the following vehicles equipped with either a GM 8L90 or GM 8L45 transmission, regardless of engine:

(though the lawsuit only covers certain models/years equipped with 8L45 and 8L90 transmissions the torque converter design defect also exists in the 6L45 back to 2013 and 2014. I had a 2013 ATS with a non-turbo base 2.5 ltr 4 cylinder mated to a 6L45 with this exact unrepairable torque converter shudder design defect. Ron Baker)


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I have a 2019 ATS (VIN 1G6AF1RX0K0128690). How can I find out the build date since it is impossible to get build records anymore online? I know it is a 2.0 Turbo 4-cyl, and has a 8 speed auto transmission. I have noticed my transmission doing the stuttering as well as long drawn out speed shifts, almost like it is hanging in gear.
 

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I have a 2019 ATS (VIN 1G6AF1RX0K0128690). How can I find out the build date since it is impossible to get build records anymore online? I know it is a 2.0 Turbo 4-cyl, and has a 8 speed auto transmission. I have noticed my transmission doing the stuttering as well as long drawn out speed shifts, almost like it is hanging in gear.
The doorjamb will give you the month/year of build, did you check that?
 

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Rick,
The 8LXX transmissions often experience an initial rough 1 to 2 shift after sitting overnight; this is due to slow initial fill of one clutch pack actuator involved in the 1 to 2 shift. The next time you start your CT6 in the morning, while the car is still stationary manually shift it from 1 to 2 and back to 1 again and see if any subsequent initial rough shift disappears. There were some cases with the Corvette where the affected clutch pack itself had to be replaced because of so many initial slippage events that it had damaged the friction material and if that happens then any shift involving that clutch pack would be affected.

These transmissions reply upon perfect timing of the releasing and applying elements so that the transmission is neither free wheeling nor applying two ranges at once during a shift. High resolution speed sensors measure shaft speed and if shaft speed ratios don't match due to a slipping clutch pack, then additional apply force is immediately utilized and this will result in a hard shift as you have initial slippage followed by a very hard lock. If the shift is simply rough, then a relearn procedure will likely fix it but if there is consistent slipping followed by a hard lock then it is likely the clutch pack has been worn past its normal service life and needs attention. If slippage continues even after maximum apply force has been commanded, then the transmission will go into protective limp mode and the TCM will request that the ECM turn on the CEL to indicate that DTCs are stored within the TCM.

The torque converter induced shudder that occurs especially with AFM equipped engines is another version of this where the lockup clutch in the torque converter allows slippages when it shouldn't causing an immediate call for additional apply force. So in AFM operation where the converter lockup clutch is being continuously modulated to reduce NVH, with wear you have an apply command that results in slippage triggering a call for immediate hard lockup which results in shudder as the sequence continuously repeats. Under some conditions even when all cylinders are active, the converter clutch is still modulated to reduce vibration and this is why some powertrain combinations are far more prone to the shudder issue than others. My C7 Z06 never sees AFM operation and it is running on the original fluid with no shudder issues while many of the base and Z51 level Corvettes that spend a lot of time in V4 mode have been through multiple fluid changes and in many cases have also had torque converters replaced because of severe shudder issues with the RPM varying +/- 150 RPM at steady state cruising speed.

Rodger
 

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Rick,
The 8LXX transmissions often experience an initial rough 1 to 2 shift after sitting overnight; this is due to slow initial fill of one clutch pack actuator involved in the 1 to 2 shift. The next time you start your CT6 in the morning, while the car is still stationary manually shift it from 1 to 2 and back to 1 again and see if any subsequent initial rough shift disappears. There were some cases with the Corvette where the affected clutch pack itself had to be replaced because of so many initial slippage events that it had damaged the friction material and if that happens then any shift involving that clutch pack would be affected.

These transmissions reply upon perfect timing of the releasing and applying elements so that the transmission is neither free wheeling nor applying two ranges at once during a shift. High resolution speed sensors measure shaft speed and if shaft speed ratios don't match due to a slipping clutch pack, then additional apply force is immediately utilized and this will result in a hard shift as you have initial slippage followed by a very hard lock. If the shift is simply rough, then a relearn procedure will likely fix it but if there is consistent slipping followed by a hard lock then it is likely the clutch pack has been worn past its normal service life and needs attention. If slippage continues even after maximum apply force has been commanded, then the transmission will go into protective limp mode and the TCM will request that the ECM turn on the CEL to indicate that DTCs are stored within the TCM.

The torque converter induced shudder that occurs especially with AFM equipped engines is another version of this where the lockup clutch in the torque converter allows slippages when it shouldn't causing an immediate call for additional apply force. So in AFM operation where the converter lockup clutch is being continuously modulated to reduce NVH, with wear you have an apply command that results in slippage triggering a call for immediate hard lockup which results in shudder as the sequence continuously repeats. Under some conditions even when all cylinders are active, the converter clutch is still modulated to reduce vibration and this is why some powertrain combinations are far more prone to the shudder issue than others. My C7 Z06 never sees AFM operation and it is running on the original fluid with no shudder issues while many of the base and Z51 level Corvettes that spend a lot of time in V4 mode have been through multiple fluid changes and in many cases have also had torque converters replaced because of severe shudder issues with the RPM varying +/- 150 RPM at steady state cruising speed.

Rodger
Thank you, Rodger. I will try that today.

Rick
 

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I have a 2019 ATS (VIN 1G6AF1RX0K0128690). How can I find out the build date since it is impossible to get build records anymore online? I know it is a 2.0 Turbo 4-cyl, and has a 8 speed auto transmission. I have noticed my transmission doing the stuttering as well as long drawn out speed shifts, almost like it is hanging in gear.
An email with your VIN to [email protected] will get you a PDF of your build sheet.
 

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This week I took my 2017 ATS 3.6 Premium Performance to the dealer for its regular service and asked them to investigate a transmission shudder. I have been having the typical "rumble strip" sensation upon light acceleration at moderate speed (20-45 mph) intermittently but fairly consistently most of the summer. I did notice it happens more often on warm days, and the day of my service was unseasonably cool. They called late in the day to say they could not duplicate it. My service advisor is very good and was aware of the bulletin, and told me when she broke the news and saw my dismay that I should bring it back the next time it does it and let her or her boss ride with me while I duplicated it, which I thought was reasonable. Today (a Saturday when they are not open for service) was a warm day and I could make it do it almost at will.Hopefully we get some warm days next week so I can demonstrate it for them. Since the car only has a bit more than 6000 miles on it I want this fixed ASAP and am hoping the new fluid outlined in the bulletin will do that.
Had the same issue with my 2016 ATS-V @ 6000. Took the service bulletin and car to my Dealer to fix. The did the suggested drain and refill the tranny and torque converter with a revised GM transmission fluid. No more issues. Have your dealer call Doug's Cadillac in Seattle for the right fix, they will be very helpful! Good Luck!
 

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Discussion Starter #19
Had the same issue with my 2016 ATS-V @ 6000. Took the service bulletin and car to my Dealer to fix. The did the suggested drain and refill the tranny and torque converter with a revised GM transmission fluid. No more issues. Have your dealer call Doug's Cadillac in Seattle for the right fix, they will be very helpful! Good Luck!
They know HOW to do it, that's not the issue. The issue is a combination of them not trying very hard to duplicate the shudder while they had the car, and them not interpreting the most recent service bulletin (which seems to clearly say to do the flush without jumping through all of the diagnostic hoops that were previously the case) in what seems to be the way it states. They insist they need to hook up the Picoscope and do all of the previous steps to document the shudder while the car is in their possession or otherwise GM will not pay the cost of the work. If they again do not reproduce the shudder then I fear I am again going to be out of luck.
 
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