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Here is the reply from Subaru:
Thank you for your email. The trailer brakes are engaged via the anti-sway system in the vehicle.

Sincerely,

Doug
Subaru of America, Inc.
Customer Advocacy Department
I really question that response. How would the native (in the vehicle) anti-sway system communicate with the trailer brake controller? They are two discrete systems...the ECU in the Ascent has no interface with whatever brand/model of brake controller you have installed. I think "Doug" needs to do some more research. Please prove me wrong, if this is true I would be pleased, however, I doubt that is the case.
 

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I really question that response. How would the native (in the vehicle) anti-sway system communicate with the trailer brake controller? They are two discrete systems...the ECU in the Ascent has no interface with whatever brand/model of brake controller you have installed. I think "Doug" needs to do some more research. Please prove me wrong, if this is true I would be pleased, however, I doubt that is the case.
There's absolutely a connection - it's the very one that allows the Ascent to activate the trailer brakes during normal human braking, as well as when the computer is handling all braking during ACC cruise, or PCB engagements.

"Doug"'s name is really Doug, btw.

What the Ascent cannot do is control individual trailer brakes like it does on its own brakes.
 

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There's absolutely a connection - it's the very one that allows the Ascent to activate the trailer brakes during normal human braking, as well as when the computer is handling all braking during ACC cruise, or PCB engagements.

"Doug"'s name is really Doug, btw.

What the Ascent cannot do is control individual trailer brakes like it does on its own brakes.
I guess I am behind the times. I've been towing for years with inertia-activated brake controllers on mostly 3/4 and one ton pickups. I don't doubt what you are saying, but if so, why do I need a separate brake controller at all, if the capability is built into the Ascent's onboard computer braking system? Correct me if wrong, but aren't the Tekonsha, etc controllers recommended here just conventional inertia-activated discrete systems?
Also, I'm not aware of any brake controller on the market that can control individual trailer brakes, it's all or none as far as I know.
 

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I guess I am behind the times. I've been towing for years with inertia-activated brake controllers on mostly 3/4 and one ton pickups. I don't doubt what you are saying, but if so, why do I need a separate brake controller at all, if the capability is built into the Ascent's onboard computer braking system? Correct me if wrong, but aren't the Tekonsha, etc controllers recommended here just conventional inertia-activated discrete systems?
Also, I'm not aware of any brake controller on the market that can control individual trailer brakes, it's all or none as far as I know.
An inertia-based brake controller (proportional brake controller) uses the vehicle's "brake-activated" signaling line in combination with an accelerometer to apply brakes based on the signaling of the tow vehicle in combination with the (change in) inertia detected being used to control braking force. When the brake is activated, the controller applies pressure to the trailer brakes depending on the tow-vehicle’s momentum.

So, short version: the Ascent triggers the braking activity, and the inertial controller adjusts braking force based on how quickly the Ascent is braking. This is also why those types of brake controllers need to be oriented facing the correct direction to properly operate.

Remember though - the brake trigger that goes into the controller is computer controlled, just like the tiny little brake lights on the dash board's center-pod display, or on the MFD's ACC display. In "old school" systems where the trigger is run right off the brake switch hooked up to the pedal, things would be different.

So... the "why (do we need a separate brake controller)" is because the controller allows regulating the trailer's braking force, instead of making it a simple on/off activity.
 

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An inertia-based brake controller (proportional brake controller) uses the vehicle's "brake-activated" signaling line in combination with an accelerometer to apply brakes based on the signaling of the tow vehicle in combination with the (change in) inertia detected being used to control braking force. When the brake is activated, the controller applies pressure to the trailer brakes depending on the tow-vehicle’s momentum.

So, short version: the Ascent triggers the braking activity, and the inertial controller adjusts braking force based on how quickly the Ascent is braking. This is also why those types of brake controllers need to be oriented facing the correct direction to properly operate.

Remember though - the brake trigger that goes into the controller is computer controlled, just like the tiny little brake lights on the dash board's center-pod display, or on the MFD's ACC display. In "old school" systems where the trigger is run right off the brake switch hooked up to the pedal, things would be different.

So... the "why (do we need a separate brake controller)" is because the controller allows regulating the trailer's braking force, instead of making it a simple on/off activity.
Thanks for the explanation, I've installed Tekonshas in the past and the only interface with the vehicle wiring aside from 12v in was the brakelight signal to trigger the unit, either "on" or "off", everything else was 100% on the controller. I guess the Ascent's computer accomplishes the same by telling the controller to "turn on" and apply the proper amount of gain to the trailer brakes?
 

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Thanks for the explanation, I've installed Tekonshas in the past and the only interface with the vehicle wiring aside from 12v in was the brakelight signal to trigger the unit, either "on" or "off", everything else was 100% on the controller. I guess the Ascent's computer accomplishes the same by telling the controller to "turn on" and apply the proper amount of gain to the trailer brakes?
No, it just tells it to turn on (the inertia based force controlling of the controller would take care of the rest) - but, my guess is that just like how the Ascent (all Subies for a long time) control individual wheels separately, it can also control the braking of the trailer separately from the car. It can't do separate brakes on the trailer, obviously, but I don't see why it couldn't turn on the trailer brakes, and apply zero to less force on the car's.

If I get some time to speak to one of the engineers or Product Team Leads, I'll dig for some technical details and share what I can.
 

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No, it just tells it to turn on (the inertia based force controlling of the controller would take care of the rest) - but, my guess is that just like how the Ascent (all Subies for a long time) control individual wheels separately, it can also control the braking of the trailer separately from the car. It can't do separate brakes on the trailer, obviously, but I don't see why it couldn't turn on the trailer brakes, and apply zero to less force on the car's.

If I get some time to speak to one of the engineers or Product Team Leads, I'll dig for some technical details and share what I can.
If the Ascent's computer could energize the trailer brakes independently of the service brakes, that would solve the trailer sway issue. However, since the controller's system is inertia activated and without the car slowing (service brakes applied), I don't see how that is possible. As I understand it, Subaru's trailer sway control is done all through the service brakes, actuated independently. If there were a way to "override" the controller and apply trailer brakes only, that would be great. I'm sure it could be done, but would require a factory designed system integrated into the overall computer/braking system. Seeing that the Ascent's job one isn't towing, it would be an expensive option not needed by many buyers.

My last truck (2014 Ram/Cummins) had a factory installed, integrated brake controller, but still had a manual slide control to apply trailer brakes independently to correct sway.
 

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That also begs the question what if you’re towing without a brake controller? I suppose the Ascent could still sent the same signal but without a brake controller installed it wouldn’t go anywhere.
 

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That also begs the question what if you’re towing without a brake controller? I suppose the Ascent could still sent the same signal but without a brake controller installed it wouldn’t go anywhere.
Correct. Unless the tech has changed radically, the brake controllers rely on inertia acting on an accelerometer to control the gain signal sent to the electric brakes. If the Ascent's computer sends a signal to a nonexistent controller, nothing happens. You can probably get away towing a light utility trailer (under 1000 lbs) without brakes, but not much more. I used to tow fairly heavy flatbed and enclosed car trailers, but no more. My current tows are two boats, one around 1100 lbs, the other around 3500. I may just go with surge brakes on the bigger boat, as electric brakes and water (launching a boat) don't mix well.
 

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That also begs the question what if you’re towing without a brake controller? I suppose the Ascent could still sent the same signal but without a brake controller installed it wouldn’t go anywhere.
Yup No brake controller....no electric trailer brakes.
 

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I would bet the ascent uses vehicle braking as do most trucks with electronic sway control. The idea from my understanding being to control where the truck is pointed not really to cause sudden slowing. How would the ecm in the tow vehicle know how much braking force to apply to the trailer, even if it could? Could the oem be assured braking the trailer axles wouldn't cause an accident in and of itself?

All in all better to control the truck and therefore the trailer as well. Nothing like thousands of pounds pulling on the hitch to get the trailer back in line. In any case the proof is in the testing.
 

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I would bet the ascent uses vehicle braking as do most trucks with electronic sway control. The idea from my understanding being to control where the truck is pointed not really to cause sudden slowing. How would the ecm in the tow vehicle know how much braking force to apply to the trailer, even if it could? Could the oem be assured braking the trailer axles wouldn't cause an accident in and of itself?

All in all better to control the truck and therefore the trailer as well. Nothing like thousands of pounds pulling on the hitch to get the trailer back in line. In any case the proof is in the testing.
I'm not familiar with the latest trucks with electronic sway control, but I've logged many miles over many years towing trailers with electric brakes. The physics are much like an arrow in flight..the fletches at the back end keep the arrow flying in a straight line. When I've encountered trailer sway, the common practice is to manually engage the trailer brakes, not the tow vehicle brakes. This drag from the rear tends to straighten out the trailer and tow rig to the same straight direction. This is obviously not to be done while cornering. If the truck brakes are applied without the trailer brakes, it just exacerbates the sway to a disastrous conclusion....the tow wants to pass the truck.
 

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I'm not familiar with the latest trucks with electronic sway control, but I've logged many miles over many years towing trailers with electric brakes. The physics are much like an arrow in flight..the fletches at the back end keep the arrow flying in a straight line. When I've encountered trailer sway, the common practice is to manually engage the trailer brakes, not the tow vehicle brakes. This drag from the rear tends to straighten out the trailer and tow rig to the same straight direction. This is obviously not to be done while cornering. If the truck brakes are applied without the trailer brakes, it just exacerbates the sway to a disastrous conclusion....the tow wants to pass the truck.
Well its always a good day to learn something new, lol.
 

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Well its always a good day to learn something new, lol.
Always good to learn a lesson...or give one. Interesting vid, all these years I've been manually employing the "AL-KO" method and never knew it had a name. I like the Bosch tech, tho I've never owned a trailer with that feature. It would need an independently controlled braking computer and actuation system, not many trailers have that.
 

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Always good to learn a lesson...or give one. Interesting vid, all these years I've been manually employing the "AL-KO" method and never knew it had a name. I like the Bosch tech, tho I've never owned a trailer with that feature. It would need an independently controlled braking computer and actuation system, not many trailers have that.
It's an aftermarket add on. My trailer had a sway command system similar to the Al-KO system. The ascent works just as well all by itself, so I removed the sway command and sold it on ebay. Your arrow analogy lacks a forward engine and doesn't account for actions that can be taken by the front of the arrow IF it had forward stabilizers and flaps, ;).
 

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It's an aftermarket add on. My trailer had a sway command system similar to the Al-KO system. The ascent works just as well all by itself, so I removed the sway command and sold it on ebay. Your arrow analogy lacks a forward engine and doesn't account for actions that can be taken by the front of the arrow IF it had forward stabilizers and flaps, ;).
Fair enuf, I recall one post (I think here) by an owner who wasn't too pleased with the Ascent system. He said that when passed by a big rig causing buffeting & sway, the system would overreact with the throttle control and slow the rig to 40 MPH on the interstate. He was concerned about being rear-ended by an 18 wheeler going 80 MPH behind him. With the light tows I'll have, and with proper weight distribution, I doubt that any sway control will be required...If so, I'll rely on my tried & true "manual AL-KO" system via the controller..;)
 

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Discussion Starter · #38 ·
A very enlightening discussion, as always. As the OP, I appreciate the information, and look forward to more details if available from Subaru. Tight integration between the controller and the electronic antisway certainly should be possible although my knowledge of this stuff is superficial. I do not see why it could not detect presence of the brake controller and send a signal to it at the same time as it selectively activates brakes on the Ascent. We just finished a 4600 km trip from Ontario to BC towing an Airstream Caravel 16. This included mountain and winter travel. I will post a description in the towing experiences section.
 

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A very enlightening discussion, as always. As the OP, I appreciate the information, and look forward to more details if available from Subaru. Tight integration between the controller and the electronic antisway certainly should be possible although my knowledge of this stuff is superficial. I do not see why it could not detect presence of the brake controller and send a signal to it at the same time as it selectively activates brakes on the Ascent. We just finished a 4600 km trip from Ontario to BC towing an Airstream Caravel 16. This included mountain and winter travel. I will post a description in the towing experiences section.
As I understand it, the vehicle's sensors can only send a signal to the controller to activate. However, the degree of gain the controller sends to the trailer brakes is solely controlled by the accelerometer within the controller. In other words, unless the vehicle is decelerating, the controller won't signal the trailer brakes to engage, or how aggressively to do so.

Disclaimer: All my towing experience has been with the traditional inertia-activated electric brake controllers (Tekonsha and the like). My last truck, a 2014 Ram/Cummins, came with a factory-installed and integrated controller. Although the truck had an electronic stability control system, it still relied on the deceleration of the truck to activate the trailer brakes and also had a manual slide to activate the trailer brakes in an emergency or to correct sway. It is certainly within the realm of Subaru's technology to design a system where the vehicle's computer could control both the tow vehicle's and the trailer's brakes as an integrated system without the need for an add-on controller.

I am eager to hear of your recent adventure, as a small TT may be in my future plans.
 

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As I understand it, the vehicle's sensors can only send a signal to the controller to activate. However, the degree of gain the controller sends to the trailer brakes is solely controlled by the accelerometer within the controller. In other words, unless the vehicle is decelerating, the controller won't signal the trailer brakes to engage, or how aggressively to do so.

Disclaimer: All my towing experience has been with the traditional inertia-activated electric brake controllers (Tekonsha and the like). My last truck, a 2014 Ram/Cummins, came with a factory-installed and integrated controller. Although the truck had an electronic stability control system, it still relied on the deceleration of the truck to activate the trailer brakes and also had a manual slide to activate the trailer brakes in an emergency or to correct sway. It is certainly within the realm of Subaru's technology to design a system where the vehicle's computer could control both the tow vehicle's and the trailer's brakes as an integrated system without the need for an add-on controller.

I am eager to hear of your recent adventure, as a small TT may be in my future plans.
Just finished a trip towing a 3500 lb tt from NC to the grand canyon and back. Grest performance with no issues. I use the tekonsha controller.
 
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