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Discussion Starter · #1 ·
I have seen various references to the electronic sway control in our Ascents (I have 2021 Premier (Canadian) with tow package), but cannot find any reference to it in the manual or searching the forum and Subaru. Since applying the trailer brakes is one way to control excessive sway, I was wondering if that is part of the algorithm. Or will that depend on the brake controller?
 

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It's built into the vehicle software. There's nothing to do...it's automatic. My understanding is that it senses excess sway and applies vehicle braking to help correct it. If a trailer brake controller is in use, it would likely sense that and act proportionally I would think. I'm just thinking this through, however, and don't know of any specific documents that describe things.
 
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Discussion Starter · #3 ·
It's built into the vehicle software. There's nothing to do...it's automatic. My understanding is that it senses excess sway and applies vehicle braking to help correct it. If a trailer brake controller is in use, it would likely sense that and act proportionally I would think. I'm just thinking this through, however, and don't know of any specific documents that describe things.
That is what I was understanding from what I have seen on this forum and others. On the Subaru of America and Canada websites, the only mention of sway (I did a general google search and word search on the sites as well), is under Eyesight Technology and it says it provides "Lane Sway Warning". It does not say what that means.

Even if automatic, it would be good to see it officially stated and described somewhere. It seems like a terrific safety feature for a tow-capable vehicle. Otherwise, I put it in the category of potential urban myth. If it does activate the trailer brake through the controller, that would also be good to know rather than awkwardly reaching for the manual button while trying to focus on keeping the car under control.
 

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That is what I was understanding from what I have seen on this forum and others. On the Subaru of America and Canada websites, the only mention of sway (I did a general google search and word search on the sites as well), is under Eyesight Technology and it says it provides "Lane Sway Warning". It does not say what that means.
The eyesight lane sway warning is different than the trailer stability assist.

From the 2019 eyesight manual:
Font Material property Parallel Screenshot Document
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The trailer stability assist has been discussed in this thread but may be worth revisiting since it doesn't appear the original question, or yours, was ever answered as to where the documentation on the Ascent's trailer stability assist is found.
 

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It's built into the vehicle software. There's nothing to do...it's automatic. My understanding is that it senses excess sway and applies vehicle braking to help correct it. If a trailer brake controller is in use, it would likely sense that and act proportionally I would think. I'm just thinking this through, however, and don't know of any specific documents that describe things.
I think this is basically correct, however I think the system in the Subaru works when it detects any sway. We also have a Ford Ranger which also has electronic sway control however that really only corrects for excessive sway. Put differently if you're driving the same trailer down the highway without additional sway control the Ascent rides much nicer. Of course the reason to get a truck is that it will accept a WDH and that works better than just the electronic sway control.
 

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Of course the reason to get a truck is that it will accept a WDH and that works better than just the electronic sway control.
Keep in mind that any sway control with a WDH is a secondary benefit. The primary reason for a WDH is to shift tongue weight to the front axle of a tow vehicle for better weight balance so that steering and braking remain "normal". WDH by itself will provide some minor sway control by itself, but there's a reason that there are sway control add-ons for WDH for folks "towing large".
 
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Keep in mind that any sway control with a WDH is a secondary benefit. The primary reason for a WDH is to shift tongue weight to the front axle of a tow vehicle for better weight balance so that steering and braking remain "normal". WDH by itself will provide some minor sway control by itself, but there's a reason that there are sway control add-ons for WDH for folks "towing large".
Good points. I came to the Ascent from a Ram/Cummins 2500 4x4 truck that I used extensively for towing 14K-15K+ trailers. I am now down to two small boats, 1500 & 3500lbs. I don't have any illusions about the Ascent being an HD tow vehicle, just hoping it will do the job it is rated for.
 

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Info is limited but it's out there... I was curious and found 2 examples. Some of the other thread commenters seem to have read this but no one linked it directly. I'm sure it's in every year version of the examples below...

2019 Subaru Ascent Press Kit:

and this 2022 brochure:
 

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I dont think you will find any documentation on how it actually works or what exactly it does. I can say it most definitely straightens things out when they get hairy, and very quickly. I felt the trailer sway hard saw a dash light flash heard a beep and then everything was fine. I unpuckered and reminded myself to move some weight forward at the next stop, lol.
 

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I dont think you will find any documentation on how it actually works or what exactly it does. I can say it most definitely straightens things out when they get hairy, and very quickly. I felt the trailer sway hard saw a dash light flash heard a beep and then everything was fine. I unpuckered and reminded myself to move some weight forward at the next stop, lol.
I saw one post that said the system is integrated with the lane keep and the ABS system. When it detects sway it engages the ABS to correct the sway.
 

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I saw one post that said the system is integrated with the lane keep and the ABS system.
I was thinking more along the lines of dynamic stability control, just extended to trailer sway when towing. It’s recommended to turn off lane keep when towing to prevent additional sway from being added when that system makes corrections.
 

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Discussion Starter · #12 ·
The eyesight lane sway warning is different than the trailer stability assist.

From the 2019 eyesight manual:
....
The trailer stability assist has been discussed in this thread but may be worth revisiting since it doesn't appear the original question, or yours, was ever answered as to where the documentation on the Ascent's trailer stability assist is found.
Thanks for that reminder about the EyeSight manual. I had looked only in the primary manual. But this one also just mentions sway warning as an indicator of fatigue. Nothing about towing. The thread also fails to actually answer the question.
 

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Discussion Starter · #14 ·
I was thinking more along the lines of dynamic stability control, just extended to trailer sway when towing. It’s recommended to turn off lane keep when towing to prevent additional sway from being added when that system makes corrections.
So this is why I think it is imperative to have something documented in the manual. Turning off lane departure also disables "sway warning", but does it disable the trailer antisway system also? I think that Subaru made a mistake in labelling the former feature "sway" because what it seems to do is warn you after a few minutes of repeated lane departures that you may be tired and should take a rest.
Info is limited but it's out there... I was curious and found 2 examples. Some of the other thread commenters seem to have read this but no one linked it directly. I'm sure it's in every year version of the examples below...

2019 Subaru Ascent Press Kit:

and this 2022 brochure:
Thanks for those links. The hard copy brochure I have for 2021 does not list the detailed specs, but I think there were no changes for 2022 so "trailer stability assist" is the term that Subaru uses.
 

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Discussion Starter · #15 ·
I dont think you will find any documentation on how it actually works or what exactly it does. I can say it most definitely straightens things out when they get hairy, and very quickly. I felt the trailer sway hard saw a dash light flash heard a beep and then everything was fine. I unpuckered and reminded myself to move some weight forward at the next stop, lol.
Good to know that it works!! I have a Prodigy P2 brake controller. It is mounted low under dash by my left leg so it is awkward to engage the manual button. Maybe I need to find somewhere safe, induce sway and see if the controller display shows it is activating the brakes :p
 

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Info is limited but it's out there... I was curious and found 2 examples. Some of the other thread commenters seem to have read this but no one linked it directly. I'm sure it's in every year version of the examples below...

2019 Subaru Ascent Press Kit:

and this 2022 brochure:
For those not wanting to read through the two linked documents, from the 2019 Press Kit: “This powertrain allows up to 5,000-lb. towing capacity, the most of any Subaru in history. Trailer Stability Assist helps to maintain vehicle stability while towing. The TSA system utilizes yaw sensors to monitor trailer sway and then can brake individual wheels to stabilize the vehicle and trailer.”. The 2022 brochure says essentially the same thing.
 

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For those not wanting to read through the two linked documents, from the 2019 Press Kit: “This powertrain allows up to 5,000-lb. towing capacity, the most of any Subaru in history. Trailer Stability Assist helps to maintain vehicle stability while towing. The TSA system utilizes yaw sensors to monitor trailer sway and then can brake individual wheels to stabilize the vehicle and trailer.”. The 2022 brochure says essentially the same thing.
Seems like a flawed approach. Trailer sway should be controlled by the trailer brakes, not the tow vehicle brakes.
 

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^^ which is why something more than an ad or brochure would be a good reference

at work I’m constantly researching parts and tech manuals. I run across brochures often. They’re useless to me — I already have the machine.
 
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