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Catastrophic Transmission Failure 2021 Ascent 10k Miles

29K views 167 replies 38 participants last post by  Robert.Mauro 
Wow, that's horrible! The good news is, in all my time learning about and following the TR690's 12 year history, you're literally the second verified chain failure (plus one unverified guess by another person) I've ever seen. That chain is literally the strongest, beefiest, highest-torque-capable CVT belt or chain mechanism put into any production car. So, I definitely think this is a one off.

I am wondering if it was low on CVT fluid or had the wrong stuff in there (eg: Jiffy Lube messed up). Otherwise, it's a freak situation that's rarely happened in all of the years the TR690 has been in service.

Once they swap the entire TR690, you'll be good as new (but remember, you have a 1,000 mile break-in to perform, with no towing during that time). I'd be very much fine with them swapping that TR690 for a new one, and dealing with any damage from bits of the CVT being ejected. I wouldn't be surprised if they offered you an extended warranty either. You still, of course, need to do what makes YOU feel comfortable, regardless of what would make ME feel comfortable. 😉

Please keep us posted.
 
But not in Ascent. It's a heavier vehicle with a more powerful engine. Even in the new WRX, the engine is detuned a bit for the CVT.
The CVT isn't why it's detuned. The 2022 Subaru WRX puts out 271 hp and 258 lb-ft of torque.

On the other hand, the Subaru WRX s4 tS by STI puts out 295 hp and 296 lb-ft torque. It also uses the TR690. 😉
 
It should not have been a factor in this transmission failure, but it was.

I doubt that. Towing should have no effect on the chain exploding to pieces. I can name a half dozen components, off the top of my head, that may experience greater wear, from towing, but the chain isn't one of them. This was likely caused by a fluke manufacturing defect in the chain, a leak, or improper maintenance (eg: Jiffy Lube draining it, or someone putting the wrong fluid in it).
 
He was towing a travel trailer up steep mountain passes. I'll bet that chain might have lasted the life of the vehicle if he never used it for towing.
That chain will never explode, no matter what you tow, from the act of towing. The over 3 dozen clutch plates, or one or both of the two differentials would go first. Or the chain would eat through the variator first.

I would bet big money it had a defect, or there was a non chain cause.
 
Editing my question, because the original question has the potential to stir shit snd that was not my intention. Are there any other factors that could cause the chain to fail aside from being defective? Clearly there must have been something else going on if the CVT fluid was overheating first.
Oh, absolutely. Lack of CVT fluid (or the fluid being very low) immediately comes to mind. It's also possible the CVT fluid was so "varnished"/"burnt" that it was no longer functioning as CVT fluid. Another component breaking and wedging between chain and variator cone at high enough speed to break the chain, maybe? I think there are a decent number of non-chain causes that may cause one of those chains to fail.

Apologies to any if my comment seemed too direct - I had a short posting window. I just didn't want people thinking the chain itself is prone to exploding, under any normal operational circumstance, or under any load.

It obviously catastrophically failed - and I am very very interested in "why?" - it's just not the design. People (especially WRX owners showing off) tow all sorts of things (like WRX owners and 18 wheelers) with their TR690s, and this doesn't happen.

Can continuous towing contribute to a CVT failure or some other sort of issue in a limited-duty-tow-vehicle, like @pro10is said? Absolutely, positively. So, is this related to towing? I'm not sure - there are people in this very group who tow more weight, through the mountains, in the desert.

So, what's the cause/determining factor? I don't know, and can't speculate.
 
The CVT puts out less than the manual, no?
Nope. There's no WRX (manual or automatic) that puts out more power than the CVT-only WRX s4 tS. And for the regular WRX series, the power output is the same regardless of if you pick manual or CVT.

For instance, here's all three trims, manual and CVT, of the 2021 WRX
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Uhh, eh? S209 puts out way more. 40+ more HP
My statement is accurate. The s209 is an STI. The WRX s4 tS by STI is a WRX with some work done by Subaru Technica. The rest of the ones I mentioned or alluded to are WRX's. No actual US market STI comes with a CVT. All WRX's come as either CVT-only or a choice of CVT or manual (same hp and torque for either).

In Japan, there's all sorts of other models, like the Levorg STI which does come with a CVT (CVT only), but that's a different story (and a lot less powerful than our WRX's).
 
Lol....you are probably then the only person that uses "WRX" literally to mean a non-STI WRX.
That's odd. Some STI owners would take very vocal offense to that (I think they sometimes go too far - heck, you should see the s***storm if they see a WRX with an STI badge), but, they're right about one thing - they're drastically different cars that look similar. Different transmissions (even the manuals of each are quite different), different engines (eg: the 2021 came with a 2.0L in the WRX, and a 2.5L in the STI), different body front end, different body rear end, different center differentials, different struts and shocks, different brake systems (calipers and pads), different steering rack and steering system, different seats, different instrumentation, different suspension parts, and on and on.

The STI is a WRX as much as the Forester XT was an Impreza (actually, the Forester XT was closer to "being" an Impreza than an STI is to being a WRX).

And besides, the STI is stick only. They didn't detune it for the CVT - there is no CVT option. 😉
 
Oh, and Subaru lists the WRX STI under the "WRX" section.....and my WRX manual is for both the STI and non-STI variant.

;)
Yep. And the Legacy and Outback share the same manual. 😉
 
Same symptoms I was having with my Ascent, the turning was really bad and also a noise coming from where the drive shaft connects to the CVT, I have had my Ascent 8 months and the car showed signs of this at 15k- I drive MANY miles a yr. The "new" transmission was placed 1500 miles ago and my 2021 Ascent is going BACK to the dealer tomorrow bc now the vehicle vibrates badly 😢. It's worse some days. The drive shift noise is also back when I shift from R to D. YOU must call Subaru of a AMERICA- make sure this complaint is logged and get a case file # continue to email or call the specific person that is assigned to you. My vehicle is 90% for work and I drive upwards of 45k a yr. I had 29k on the vehicle when FINALLY got CVT replaced. I had to kick and scream to get the one dealer to test drive it and they basically said this is "how the CVT" runs. When I could barely get my car out of a hospital parking garage trying to get to a very sick patient at another hospital... I went to a new dealer and they diagnosed. It's been a struggle as this vehicle is my lifeline for my emergency medical device job. My 2015 RAM Diesel runs smoother than my Subaru
Probably the AWD transfer clutch.
 
Hi Yoshi! This just came out - remember when I said something inside the CVT breaking and running under the chain may cause it to snap? 😞

2021 isn't supposed to be a part of this, but, if your build date was July 20, 2020 or earlier, perhaps yours was part of this.

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Our first Subaru, a 2017 3.6r Outback, made us realize why people speak so highly of the brand. The car never gave us any issues, tore thru mountain passes, snow banks, and would perform like a champ off road. So when the time came to replace a second vehicle we wasted no time shopping other brands and purchased a 2021 Ascent Touring back in December of 2020. Once we took ownership of the vehicle we installed a 1.5" lift kit from Anderson Design Fabrication, changed wheels and tires, added primitive skid plates underneath the vehicle, as well as a rally light bar along with rally lights.

Our first indication our Ascent was experiencing transmission issues was back in May. We live in Los Angeles and own a small teardrop trailer that we had been pulling with the ascent. On several occasions, all of which occurred when climbing mountain passes, the cvt fluid overheating light had come on requiring us to pull off to the side of the highway in order for the fluid to cool prior to resuming our travels. Upon returning to town I brought the vehicle in for service and advised the Subaru service department of the issue and asked that they look in to the cause. Service department informed me that everything checked out and they did not see an issue with the vehicle.

Wednesday a week ago, myself, wife and five year old had the ascent packed with camping gear and headed north for a weekend up in Big Sur. It was mid afternoon on a relatively cool day as we started climbing the grapevine, a notoriously steep climb out of Los Angeles that takes you up central California. As the vehicle was climbing the pass I felt the transmission slip as it aggressively shifted gears (another complaint I have of the vehicle due to its small engine). Within two minutes of that slip all three of us hear a loud boom, my eyes immediately look thru rear view mirror to see a cloud of smoke and debris bouncing across the freeway that clearly came from our vehicle. We lost complete control over the vehicle and coasted while making our way to the shoulder.

Subaru road side assistance was unable to get us a tow truck in a reasonable time frame so I used my AAA membership to have us towed back to our house so I could transfer our gear to the outback and get us out of town for the weekend. Once we returned home I had the Ascent towed in to our Subaru dealer who now has the vehicle and awaiting an engineer from NA Subaru to inspect the, as the service manager classified it as a, catastrophic transmission failure. From what they informed me after inspecting the vehicle was the CVT chain broke off and literally blew a hole thru the transmission casing (photos attached). He also stated that after all his years in service he has never seen anything like this occur.

The first thing my wife asked was, did you tell him we want a new car?

Now I know the service manager is not the person to make that decision, but wondering if there have been any other cases where this has occurred in a vehicle less than a year old with less than 12k miles. Do I really want to have our vehicle repaired? We no longer want the vehicle and plan to sell it regardless once the repairs are made.

UPDATE 11/3: Dealer was instructed to wait on repairs for an engineer from SOA to visit and inspect vehicle. This afternoon SOA authorized the replacement of entire Transmission, and the Transmission Control Module.
 
As a recall, affected vehicles will receive the rapair whether symptoms have arisen or not?
We probably have to wait for the actual recall announcement for the proposed remedy.
If I were to make a totally personal guess, based on my understandings of the system, if a CVT has not been negatively affected, reprogramming it is the solution. If it has (which could be determined using an SSMv4 and monitoring the signals from the TCM under the conditions that would cause the pressure variations), then, determining if a chain slip has occurred would be next... No: reprogram... yes: replace.

But, yes, all vehicles that have the incorrect programming will be repaired in one fashion or another.
 
For those reading it, "fragments of the chain guide can inhibit shift selection mechanism" most likely means that chunks of the chain guide can jam under the chain between it and a variator cone, preventing the chain from riding down into the cone valley, and potentially breaking the chain in the process.

AND, once again, it turns out to NOT be the TR690 itself, but electronics/programming. 😕
 
My 2021 Outback XT was born only a few weeks after the end date.
Fortunately, Subaru is ridiculously thorough about tracking every aspect of a built, so, you lucked out.

I wonder if this will get extended to the 2021 and 2022 models. I came across a service bulletin about diagnosing chain slippage and replacing transmissions if found, which has been expanded out to 2022 models.
The Diagnostics TSB was expanded to 2022 because the diagnostics procedures also apply to the 2022 TR690 (which, other than programming, is the same as the 2019-2021 TR690). So, good news is, that's not indicative of (or relevant to) the likelihood the campaign will be expanded. If it is expanded, it's not related to that TSB.
 
I haven't noticed those to date. In "D", the CVT acts like an old Buick Dynaflo or Packard Ultramatic....just a smooth take-off with no perceptible "shifts". When do the fake shifts occur?
Floor it. 😉
 
Only 300 miles on the clock, not ready to wind it up tight yet :oops:
Oooh, yeah, don't floor it... yet. 🤣

But, once you hit 1,000 miles... 😉
 
Robert, this is disingenuous. Without programming, the transmission will not function. I'm disappointed that this is your position.
Alas, there's nothing disingenuous about it. The TR690 design is solid, and nothing in the design is the cause of it. It's the application, as controlled by things external to the TR690 that is at fault. This is similar to when someone does a Stage 2 tune on a WRX and destroys the TR690. The engine makes the CVT work as much as the TCM programming makes it work. The engine and ECU are as much or more involved in CVT actions and/or control than just the TCM.

Here's another analogy that may be helpful. I can buy the best gaming computer there is, with the best CPU. But, the board manufacturer, or myself, can go in and set a clock speed or timing profile that's beyond its designs, and burn out the chip - the chip isn't at fault for the software (BIOS code) that caused it to burn out.

The TR690 was never designed to have pressure "stuttering" up and down - that's a bug/design flaw in code that's external to the CVT.

So, I stand by my position. A programming flaw, outside of the CVT, caused the CVT to malfunction in a way that ends up damaging it. That's not a flaw of the CVT - it's a flaw in the TCM code, in the very much totally separate TCM mounted in the engine bay, that's telling the CVT wrong things to do. There are many dozens of TCMs and hundreds of TCM programs over the last 12 years for these CVTs - they are separate from the CVT, just like the engine is.

Any root cause analysis would show the cause to be external, and the issue to not be the CVT, but instead the program.
 
We're gonna disagree on this. When a chain changes speed it slaps. Ever look at a motorcycle chain while the bike is going through the years? The chain guide in the CVT will have to absorb the slap.
And if the TCM programming doesn't set the chain clamping pressure correctly, allowing the secondary pulley speed to fluctuate because of it, then, it's theoretically possible to both slip the chain and break the chain guides.
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Once that happens, bits of chain guide can run under the chain, and prevent the chain from riding down a fully (or mostly) opened variator pulley.
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Given the pics of the chain, there has to be a serious design flaw if the chain can slip. That is obvious to me.anyone else?
The chain tension is maintained by hydraulic force on the variator. When that force is maintained, the chain will not and cannot slip. The engine will stall before that happens.

If there's a bug in the code preventing the hydraulic clamping force from being steady or as high as it should be, then the chain will slip.

Design flaw generally means hardware/mechanical
Bug/error generally means software.

The issue in the Subarunet notice is software related. There's no design flaw in the TR690 - and the TCM is not a part of it; it just controls it, in conjunction with the ECU. Kinda like how the gas pedal is not the engine or a part of it; it just controls it. Just like how the ECU is not the engine, the engine harness is not the engine, the gas pedal is not the engine. The TCM is not the TR690.
 
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