8480818 is not a TSB, that is the dealer use billing code for warranty reimbursement under TSB 18-NA-355.

Coupled with your dealer wanting to up-sell you on using an additive (commonly known as "magic mouse milk") to "clean your transmission internally" shows that you really want to use a different dealer next time. A properly done fluid exchange is all that is necessary and using any type of internal cleaning solution on a transmission that is not being rebuilt would be a very bad move. I suspect that this special additive is something whose only distinguishing characteristic is it doesn't do any damage as its only useful feature.

I have the 8L90 (big brother to the 8L45) in my Corvette Z06 and it has worked perfectly living behind a 650HP supercharged V8. The only issue it has exhibited was the initial rough 1 to 2 shift after sitting overnight, avoided by manually shifting to second and back to first with the brakes on during the first start of the day. It got the new fluid change last year at my dealer, a painless process from a dealer who doesn't try to play games.

Rodger

 

Yes, it did not make any sense to me why it was suggested I had to pay $175 for a factory-mandated warranty service? If the additive did any good, why would GM not include that in
the TSB instructions? It get's frustrating, you think you found one you can trust but then it still goes south....anything non-warranty, I go to third party.

 

I randomly came across this thread and the info about the TSB was just want I needed. My mothers CTS has this rumble issue and I've been meaning to drop it off at the dealer but was wondering how I would describe the issue but having a tsb number makes that so much easier. We also need the rain sensor replaced again because its leaking down the windshield again. Hopefully its an easy fix and the dealer doesn't try to be shady, plus I need to bug that dealer on the replacement taillight for my 5BW that was probably scuffed in shipping. They ordered it but had no timeframe.

 

Hey all... My sister has a 2017 ATS sedan that was experiencing shudder soon after she bought it. It's certifed pre-owned and I rode in the car while it was happening. She brought it to the dealership and had it fixed under warranty. My 2016 ATS coupe also had the shudder, so I looked at her receipt to see what they had done to fix it. I see they changed the fluid out for the new fluid and replaced both the internal and external transmission harnesses. It's been over a year and no shudder on her car yet.

 

I just had this TSB performed at my local dealer and the good news is it fixed the shudder. The bad news is they told me it isn’t covered under any warranty, not even drivetrain or CPO (the CPO just expired last month grrrr). The car is 2017 and has 42K miles. Why isn’t this covered under drivetrain warranty? I’m out not quite $2K because coincidentally the tech said the temp sensor was faulty and it cost over $1.3K to replace that trans temp sensor and its integral wiring harness. Is this legit not under any warranty?

 

My dealer told me it is covered under powertrain warranty

 

Contact Cadillac division customer service also (NOT the dealership) to open a case. They may work with the dealer to cover part of the cost since your vehicle was only a month out of powertrain warranty AND the 8Lxx shudder is a very well known problem.

Site Maintenance

Rodger

 

Thanks

 

You are welcome! And if you get shuffled into a bureaucratic loop, you can always directly email the CEO at GM world headquarters. She won't answer your email directly but there are some very capable staff assistants who are pretty skilled at separating significant customer service lapses from the mundane unhappy customer and that can prove helpful.

Given the magnitude of complaints with that transmission with its "squashed torque converter", GM has been pretty responsive in making certain that customers get the fluid service. I love the 8L90 in my 2016 Corvette Z06 but it was never allowed to go into the converter clutch eating V4 mode and it has the latest fluid in it. The Corvette was particularly susceptible to shudder with the earlier fluid spec because unlike other GM products, it uses a pair of air to fluid heat exchangers to cool the transmission fluid instead of using an engine coolant to transmission fluid exchanger; the latter helps to heat the transmission fluid during short drives in cold weather operation to reduce the troublesome moisture buildup which causes converter clutch shudder while the Corvette fluid remains extremely cool until it is driven hard.

Rodger

 

I had the transmission fluid flushed and replaced in my 2017 2.0T two years ago and it greatly reduced the shudder. However, lately I've noticed it returning and I'm now out of warranty. I'm actually more aggravated by the rough 1st to 2nd gear shift under light throttle that didn't seem to be improved by the fluid change.

 

If you read this link if tech didn't reset base as in article along with fluid change you might have problems you're stating.
Gears Magazine - What is Causing that? A Look at the GM 8L90's Most Common Concerns

 

Melze,

Even after transmission service, this is a good practice with 8L series transmissions for the first start of the day. A clutch pack actuator used for the 1 to 2 shift has a slow initial fill and doing the 1-2-1 shift with the brake engaged and engine at curb idle allows it to fill during a no stress shift and the rest of the shifts for the day should be fine.

I don't believe GM ever addressed this in software for some unknown reason; when Detroit/Allison was still part of GM, the Allison "world" series 5 and 6 speed transmissions had this issue after revised hardware around 2000 with the initial 3-4 upshift and Allison released revised software that did a actuator partial prefill at engine start.

These GM transmissions are adaptive learning transmissions and once they get past the initial fast learn phase, they stay in slow learn for the life of the transmission in order to adapt to wear of the clutch packs. But if the transmission over time has learned a very bad habit then the dealer can put it back into fast learn mode so that the problem behavior can be resolved. This fast relearn will NOT overcome the slow initial actuator fill but it will allow the transmission to quickly learn to avoid issues with clutch apply/release timing and force which will lead to bad shifts that continue after the initial shift of the day.

Rodger

 

My dealer could not resolve my torque converter shudder. I was able to resolve it myself however. I traded it in

 

Ron,

I can't remember which year you owned but as I recall you had one of the earlier models with the 6Lxx series transmissions and these aren't known for shudder issues like the 8Lxx with its squashed converter. The 6Lxx series was a very well designed and tested series that was also used by BMW in several of their models. It sounds like the dealer (and maybe Cadillac division) dropped the ball on that one because your car either had an internal transmission defect or an issue with the engine/ECM that created the shudder issue and it should have been quickly resolved.

A good dealer tech makes all of the difference but GM customer service used to be a great backstop for failures at the customer/dealer interface. 20 years ago I ran into an issue with a two month old Chevy Impala that would set a DTC for a wheel speed sensor every time it rained. The dealership replaced the sensor twice and then decided they needed to replace the entire rear wiring harness which would have been major surgery.

I contacted the Chevy zone office and the rep intervened and opened a tech support case. Four hours after I initiated contact, he called back to tell me the problem had been resolved. The dealership personnel were replacing the sensor on the wrong side, the Chevy tech rep told me that they can only do so much in providing clear explanations of the DTC in their service literature and they falsely assumed that the dealership service personnel would know the difference between their right and left hands 🤣

The Chevy zone office extended the bumper to bumper warranty out to 5/100K to make up for the inconvenience which was a nice service recovery and the way GM used to do things. Sorry you had such a bad experience Ron.

Rodger

 

Thanks Rodger, I really liked the ATS and would likely have given Cadillac another chance with the CT4 - 5 but wasn't a fan of the new design. I really didn't agonize too much with my car. The Mercedes dealership gave me a great trade in price and didn't even drive it. Seems vehicles are such a commodity anymore nobody seems interested in anything but the valuation algorithm anymore.

 

Ron,

I hear you on the CT4. I went in to place an order for one and after driving the 2.7 I4 turbo I decided that it was the proper engine for a pickup which was the original intent. I was OK with the overall CT4 design but I hated the way the 2.7 felt so I ended up ordering a 2021 Camaro from the same dealership with the tried and true 335 HP 3.6, it is a very smooth running engine designed for 87 octane and really plays well with the GM/Ford JV 10 speed auto.

I will probably return to the Cadillac fold for my first electric daily driver in a few years depending upon what they produce but I have no desire for a crossover/baby SUV or whatever the current jelly bean shape/style is called by that point

Rodger

 

or whatever the current jelly bean shape/style is called by that point

😀

 

I had the shudder issue and had the fluid flush done under warranty in the beginning of August. Today my check engine light came on and I took it to a nearby Cadillac dealer to have them get the codes (different dealer, I moved). They said the codes were for Transmission Control Module and Transmission Fluid Temperature Sensor. They have me scheduled for a service appointment 7am on January 3rd. They said they couldn't guarantee it would be covered under warranty until they did a diagnosis on that day. Any thoughts or suggestions?

 

I would just let it work and see what happens. Being it was documented, and you have work orders from previous work they should warranty. Good luck

 

Do you think it's okay to wait that long? I don't notice any change other than the light... Thanks for answering it made me feel better.

 

Can you reset the code and see if it returns? I had this exact problem and the harness in question was backordered. I reset the code and during the six week wait for the harness it never returned. Seeing as to how often this is coming up on the forums it may be related to the flush and is actually a non issue. By all means get the service done, but for peace of mind until you can do it, see if you can kill the code and see if it returns.

 

As long as the transmission isn't acting noticeably different, it won't be any problem driving it until the dealer can get it in for a checkup/repair.

I suspect the only relevant code is for the temperature sensor. When any transmission trouble code is set, the TCM requests the ECM to turn on the CEL and the generic P0700 will be set in the ECM which is just a placeholder that tells the technician that one or more codes are set in the TCM.

GM automatics of the last few decades have different degrees of protection/limp mode and if the temperature sensor is providing no reading or one that is implausible based upon other conditions then a code is set and the reading is ignored. The transmission fine tunes some shift operations based upon fluid temperature and also protects itself if the temperature begins to rise. So without a valid temperature reading, part of the shift "quality" algorithm is based upon a default normal temperature so it is possible shifts will be a little less smooth-particularly with fluid that is very cold or very warm.

To avoid creating stress on the transmission, avoid full throttle starts and downshifts if possible until it is repaired.

The transmission will go into further protective mode when necessary. Shortly after I bought my 2016 Corvette Z06 I also purchased a Range anti-AFM module to keep the V8 engine from going into V4 mode. There was a random conflict that occurred between the Range module and the activities going on within the car's network during initial startup and on rare occasion that would cause the TCM and ECM to lose communication; the cure was to restart and starting and then plugging the Range module in always avoided the conflict. But if you drove it after the communications loss the vehicle was still operable but you only had reverse and one forward gear available which protected the transmission since its TCM couldn't request a power reduction from the ECM during shifts. It is possible to damage these modern automatics but GM builds a lot of protection into the programming and short of a major parts failure it won't leave the owner stranded on the side of the road.

Rodger

 

My shudder started around 50-60k kms. Had the TSB performed which swapped out the hydroscopic OEM fluid to the new M1 LV ATF HP. It was like a new transmission after and has shifted perfectly since, currently at 110K kms.

I do plan on a dump and fill every 50K kms now with the same fluid, which I hear takes about 6 quarts. Which reminds me... I'm due.

 

Dealer performed the double flush and fluid replacement today. It's immediately fixed the shudder. Covered it under the warranty too.

 

My 2016 3.6 AWD Coupe got the shudder last week. The car has 45,000 miles on it. Contacted my dealer and was told it will be $700+ to perform the TSB. Is this something that a reputable auto shop can perform using the above mentioned fluid?

 

You might try different dealer also ask service manager to get with GM for help with charges since this is ongoing problem with this transmission. I would doubt independent would have kit that is in TSB but you may find one.

 

Thanks nstar. I just reached out to Cadillac directly to see if they can work something out with the dealer.