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Discussion Starter · #1 · (Edited)
RECALL: WRK21 / NHTSA Campaign 21V955000 - Ascent CVT Chain Slip/Chain Guide Breakage
  • UPDATE:
    Due to part shortages, the remedy is expected to be available in limited quantities beginning in August 2022.


  • Type: Safety
  • Safety Recall: WRK21
  • NHTSA Campaign: 21V955000
  • Date: December 9, 2021
  • Title: Ascent CVT Chain Slip/Chain Guide Breakage
  • Remedy: Open - remedy not yet available

RECALL DOCUMENT FILES:
4 Affected Products
Vehicles

MAKEMODELYEAR
SUBARUASCENT2019-2020
SUBARULEGACY2020
SUBARUOUTBACK2020
14 Associated Documents

Canadian Owners:

About the new TCM code:
  1. Shift dynamics (I just made up that term, but you get the meaning, I hope) aka shift logic, are changed (improved)
  2. AWD transfer clutch TCM code is updated for smoother operation
  3. Variator pressure regulation code has been changed to ensure variators are fully at clamping pressure (based on torque input) before the forward/reverse changeover mechanism engages the forward clutch
In more detail:
  1. This will address some complaints of how the car shifts (too harsh, at odd times, etc)
  2. This will address the few complaints about shuddering when going around turns, as well as (though not specifically spelled out someplace you all can see) it will address shuddering issues where the rear wheels are taking up a bunch of the drive load when going straight.
  3. This will prevent the chain guide from being damaged, as well as prevent chain slip caused by incorrect variator clamping pressure when the forward clutch is engaged
What it won't do:
  • It will NOT get rid of the chirp. It's a part of how the system is designed.
  • It will NOT fix an already damaged AWD transfer clutch - that will need to be replaced in conjunction with (or after) the reprogramming.

NOTE 01:
The NHTSA Summary was poorly written by NHTSA and confusingly describes the situation. By "improperly secured chain" they mean that the programming doesn't properly set/maintain chain clamping pressure.

NOTE 02:
All
Subaru Ascents that had the previous CVT programming/chain slip recall completed are a part of this recall.

Description
Subaru of America, Inc. (Subaru) is initiating a new safety and emissions Recall for certain 2019 - 2020 model year Ascent vehicles, 2020 model year turbo Legacy vehicles, and 2020 model year turbo Outback vehicles in which the Continuously Variable Transmission (CVT) chain may slip and/or break.

Safety Risk
Due to an improper program, the CVT chain may slip, resulting in breakage of the chain guide. If the chain guide breaks, fragments of the guide could inhibit the shift select mechanism. If the vehicle continues operation with the drive chain slipping, over time the CVT drive chain could break.

Remedy
For all potentially affected vehicles, Subaru dealers will reprogram the TCU. The historical TCU data will be analyzed for chain slip characteristics and the chain guide will be visually inspected. If vehicles are confirmed to be experiencing drive chain slip or if the chain guide is damaged, the transmission assembly will be replaced. For each potentially affected vehicle, all remedy repairs necessary will be completed at no cost to the customer.

Notifications
As required by Federal Regulations, everyone will get physical old-school mail notifications from Subaru of America, within the NHTSA required notification period - and then receive app and head unit notifications.

If you don't feel like waiting to find out, you can check online on Subaru's website.

WAIT:
The remedy is supposed to be available April 2022 May 2022?. Due to part shortages, the remedy is expected to be available in limited quantities beginning in August 2022. As I'd said earlier, my expectation was that Subaru needs the time to release the final programming and get enough of the test tools to all dealerships. That's confirmed in their letter to NHTSA.

Cause Information:
Due to an improper program, if the shift select was moved to drive or reverse (D or R) immediately after the engine was started, the independent secondary pressure control program may allow the forward/reverse clutch (“F/R clutch”) to begin engagement before enough secondary clamping pressure has been applied to the drive chain.
Short version: instead of surge filling the pulleys and then engaging the forward/reverse clutch, it engaged the clutch that sends power through the variators to wheels early.

CHECK YOURS HERE:

CarFax, KBB and the other sites are NOT fully accurate. The only accurate places are Subaru Recall page (link above), Subaru app (once physical notifications are sent), and NHTSA.

More details to follow soon...

Incidentally...
Mine is one of the affected cars.

THERE ARE ONLY THREE CATEGORIES...
@E-EC-ECU perfectly describes the three categories those of us with 2019 and 2020 Ascents fall into

(2021+ Ascent owners have the new programming, and this doesn't apply)

Here's what he wrote, below:

There are three categories of people when it regards to your Ascent and this recall. Just three!
1.) Your car is exhibiting the same behavior advertised in the recall for a slipping CVT chain and/or the guide has been impacted and/or broken off. Or, your transmission is a complete mess and your car is "undriveable".

  • For these folks ... take your car in to the dealership to get inspected and fixed. If it is actively slipping the CVT chain and the transmission is not performing correctly, Subaru will replace the CVT.
    • Yes, you will get a new CVT WITH the new programming as it has already been made available (thanks @Robert.Mauro). If it is a completely separate issue and is still undriveable ... they will fix that too (just like they have been doing for 3 years now).
2.) (My situation) Your car exhibits some "weird" behavior from time to time (rpm instability, shuddering, "searching for gears"), and you think, "heck this might fix all of that".

  • For this set of people ... keep driving your car and take it in when the recall is made available to you.
    • BUT ... If this group ever finds themselves in a situation where their CVT fails and they are now a member of Group 1 (above) ... TAKE IT IN. They aren't going to wait for this recall to fix your car if your CVT is shot. The recall is about inspection subsequent repair if diagnosed. It does not delay any repairs for a known issue.
3.) (These folks I truly feel sorry for) Your car exhibits ZERO indications from this recall, and you are trying to sell it.

  • Not much I can say about this group because the used car market is so high right now, and to NOT be able to sell a car based on a recall that can't be fixed yet is unfortunate .. to say the least. I feel for this group.
The main thing to remember is that this recall is to inspect and diagnose all the potential vehicles impacted by this particular set of circumstances. Hence the tools and equipment being manufactured and delivered to simply make this inspection. If you won't drive your car because of the faulty transmission with a thrown guide arm and other major problems, this recall is completely secondary to your current situation. The recall is simply to inspect the transmissions of applicable cars and proactively replace any CVT that shows indicators.
Basically, if your transmission is a major problem right now, go get it fixed. They aren't going to reference this recall when trying to delay any fix. This recall isn't about the actual transmission repair (CVT replacement), rather it's the inspection and analysis to make sure they catch all transmissions that are exhibiting the behavior. Then, applying the actual repair.
 

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Discussion Starter · #4 ·
I'm in the recall group. Anybody know if I can go ahead and schedule service even if it's not showing on mysubaru yet?
I do not believe you can yet. Once the "remedy" (likely the reprogramming file) is ready.
 

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Discussion Starter · #6 ·

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Discussion Starter · #9 ·
Maybe a dumb question, but what does the TCU do? Seems interesting reprogramming that is a possible solution and I wonder what changed for the '21+ MY builds.
It tells the CVT what to do. So, short version is, the ECU tells the TCU "hey, here comes 231.7 lb-ft of torque". The TCU does some math and says "ok, the chain clamping pressure needs to be ###psi" and sets the pressure.

In this case, the ECU calls for a shift, the TCU does some math, sets pulley ratio and relevant clamping pressure. Instead of setting the pressure steady, it's setting it wrong, and/or jumpy, and/or low, allowing the chain to skip or slip.

When the chain does that, it can break the chain guide. I'd surmise that the chain constantly being jerked extra taut and then loosened, and/or a chunk of a broken chain guide running under the chain onto the pulley, when the chain is riding closer to the center of the pulley, can cause the chain to break.

In either event (chain slip, or chain guide broken), the CVT will get replaced.
 

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Mine gets the nod for this recall. I haven't noticed any issues, but the nice folks at my Subaru dealership will get to run the diagnostics, etc., when the time comes.
 
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Sadly my Subie is a part of this too :(...any thoughts on what the symptoms I should be watching for, so I can inform the dealership when I take it in.
Also, any ideas when the repairs will start? I got an oil change coming up this week, wondering if they might take care of it then already...

Thanks so much for posting this...appreciate the heads up.
 

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Discussion Starter · #13 ·
Sadly my Subie is a part of this too :(...any thoughts on what the symptoms I should be watching for, so I can inform the dealership when I take it in.
Also, any ideas when the repairs will start? I got an oil change coming up this week, wondering if they might take care of it then already...
I wouldn't expect them to be taking care of it this week. If you've ever felt a clutch skipping, I think one of the symptoms feels like that.
 

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Also, any ideas when the repairs will start? I got an oil change coming up this week, wondering if they might take care of it then already...
Not a chance you'll get it that fast. I actually hope they take their time and get the programming spot on before deploying it. :)
 

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Thanks for the info and link Robert. My VIN is included in this recall as I expected it would be.

Haven't had even a hint of any trouble so far, the CVT is always butter smooth.

I appreciate Subaru's attention to these potential problems.
 

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Why am I excited that mine is included?
Probably for the same reason I'm excited that mine is included...it's our first and best shot so far at a program update that might correct some of the "inconsistencies" that some of us experience with our transmissions. If it's due to a programming bug/error, and those inconsistencies are the symptom of a small amount of chain slip under certain conditions, then this is our best shot at getting it resolved.

Our dealer has looked at "shuddering" twice on our car and was not able to replicate. I really hope this resolves those cases.

Thanks for the update on this, @Robert.Mauro .
 

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It tells the CVT what to do. So, short version is, the ECU tells the TCU "hey, here comes 231.7 lb-ft of torque". The TCU does some math and says "ok, the chain clamping pressure needs to be ###psi" and sets the pressure.

In this case, the ECU calls for a shift, the TCU does some math, sets pulley ratio and relevant clamping pressure. Instead of setting the pressure steady, it's setting it wrong, and/or jumpy, and/or low, allowing the chain to skip or slip.

When the chain does that, it can break the chain guide. I'd surmise that the chain constantly being jerked extra taut and then loosened, and/or a chunk of a broken chain guide running under the chain onto the pulley, when the chain is riding closer to the center of the pulley, can cause the chain to break.

In either event (chain slip, or chain guide broken), the CVT will get replaced.
Thanks for the information - pretty interesting! Does that suggest then that one could/may feel a difference between driving a '19-'20 vs '21+ MY build due to the programming?
 

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Discussion Starter · #19 ·
I'd think that they'd feel different potentially, but that unless a 2019-2020 exhibited the fault symptoms, one wouldn't feel that difference.
 

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For what it's worth, the 2021 Outback XT loaner that I had a month or so ago drove pretty well compared to our Ascent. I wrote about it a little bit at the time. Our Ascent drove better after the TCM relearn they did, but it's mostly gone back to what it was doing prior to the relearn. I wonder if some of the stuff I feel in ours is due to small chain slip events that weren't really a factor during the transmission's relearn due to very conservative baseline values...the small slips not significant enough to cause a massive squeal event, but just enough for a momentary impulse...I wonder if all of that will be cleaned up with the revised program and the Outback XT is really what my Ascent should drive like...

I can't lie -- I'm pretty excited for this recall.
 
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