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Alrighty,
I'm uploading a video to youtube that documents all of my testing and my little DIY fixes, but Ill go ahead and summarize here:

the RAB system is able to tell if there is a bulky object (a.k.a trailer) right behind the center of the vehicle, but it's not very good at it, and needs some help. if you have a trailer with a lot of bulky stuff on the tongue (like a motorized jack or propane tanks) the Ascent will "see" it and disable RAB. same goes for a lot of the chunkier Bike racks out there. if you have something small or thin hooked up to the ascent, or you're using a hitch with a big drop, the RAB sensors won't "see" it right behind the vehicle, only the body of the trailer further back, which RAB will then treat like an obstacle and will intervene.
this explains why RVers and other "bulky trailer" towing folks haven't had this issue, whereas anyone pulling a boat trailer or a utility trailer probably has.
Supposedly, if the vehicle sags (detects a "change in ground clearance", per the owners manual) enough due to load, It will auto-disable RAB for that reason alone, but not everyone is pulls a 4,990-lb trailer with a 499-lb tongue weight, so this information isnt practical as far as disabling RAB by default for Everyone's trailering needs...

now for solutions:
step 1. go into your i/Set menu in the gauge cluster with the ascent in PARK. page 5/9 is for RAB settings, go down to disable the sonar beeping noise thing. exit.
step 2. you've got options:
-if you slap some cardboard on the tongue of your trailer or on your hitch itself, (provided the piece is big enough) RAB will pick it up, and auto-disable. you can do this just to your hitch even without a trailer connected with minimal tongue weight. I cut out a 12x18" piece of Coroplast and zip-tied it to my dropper hitch. works like a charm. makes the most sense to me if you have more than one trailer, even if you also need to do this mod to multiple hitches.
-if you're really desperate, or just hate RAB in its entirety, you can tape over the RAB sensors on the bumper, leaving a little bit of air gap between the tape and each sensor, and RAB will think it is mud or snow and auto-disable, as its stated in the owners manual. Woo, duct tape on a $35-45k car...
-if you are looking to add any accessories to your trailer (spare tire carrier, electric jack, propane, battery, toolbox, etc...) consider SAFELY adding that item really close to the front of your trailer (based on my testing it should be no further than 17" away from the bumper of your ascent to be considered a "trailer" by the RAB system) if you only have one trailer, this probably makes the most sense.



I would suspect if there's any sort of mid-cycle refresh coming, they're going to toss in that 12 inch screen, which, for all of its flaws, does have the option to permanently disable RAB in the Outback/Legacy, but idk if that would also require an updated BCM or ABS module.

looking forward to the community improving on my methods and conclusions so we can all learn something!
ive recorded all of my tests and their results in this video, along with a better explanation of the proof-of-concept coroplast plate I attached to my dropper hitch.
 

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Discussion Starter · #62 ·
Wow! Thank you, thank you, thank you!

It is my belief that the Subaru engineers really messed this RAB system up by not having a physical button that you can push to disable the RAB or automatically disabling the RAB when the 7-pin or the 4-pin connector is connected to a trailer. The virtual button on the head unit works for me only some of the time, and I have the same problem with ALL touch screens.

I have an 18" wide propane tank cover on my Apex Nano 187RB and it sets just over 17.5" from the bumper, per your demonstration for measuring, and RAB is NOT disabled when I hook up to the travel trailer.

My driveway is on an incline like yours, which has been causing me endless problems when trying to back my trailer into the drive.

I already carry painters tape in the glove box of my Ascent Premium, so I'm planning on folding paper to put over the sensors and then putting tape across the paper to hold it in place, as you demonstrate as a temporary fix when I park my trailer at home, or have to back into a camping spot.

Thanks again, so very much, for taking the time to look at a problem that I feel should never have existed.
 

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ive recorded all of my tests and their results in this video, along with a better explanation of the proof-of-concept coroplast plate I attached to my dropper hitch.
Thank you for taking the time to research this and making the video. It certainly sheds some light as to why RAB sometimes turns itself off and sometimes does not.

It looks like the Subaru engineers made an attempt to auto-disable RAB but did not put enough time and effort into it to come up with a proper algorithm for typical circumstances. This could possibly be vastly improved with more research followed up with a software update.
 

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Wow! Thank you, thank you, thank you!

It is my belief that the Subaru engineers really messed this RAB system up by not having a physical button that you can push to disable the RAB or automatically disabling the RAB when the 7-pin or the 4-pin connector is connected to a trailer. The virtual button on the head unit works for me only some of the time, and I have the same problem with ALL touch screens.

I have an 18" wide propane tank cover on my Apex Nano 187RB and it sets just over 17.5" from the bumper, per your demonstration for measuring, and RAB is NOT disabled when I hook up to the travel trailer.

My driveway is on an incline like yours, which has been causing me endless problems when trying to back my trailer into the drive.

I already carry painters tape in the glove box of my Ascent Premium, so I'm planning on folding paper to put over the sensors and then putting tape across the paper to hold it in place, as you demonstrate as a temporary fix when I park my trailer at home, or have to back into a camping spot.

Thanks again, so very much, for taking the time to look at a problem that I feel should never have existed.
looking forward to hearing how it goes for you!

Having RAB monitor the trailer wiring would make a lot of sense, although I suspect that with modern LED power draw being so low on some newer trailers, it may be difficult to detect. Certainly with braked trailers with bigger power draw or battery charging off the 7-pin though.
 

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I hear you, I have to deal with this whenever I use my boat trailer or even my bike rack. It's as maddening as the radio that won't shut up.

I've not found any way to shut the RAB off other than to hold down the touch screen for around four seconds, which is ridiculously long and unnecessary. And you're right, it doesn't always work, touch screens were not designed for long presses. And even if you manage to shut it off, it doesn't always stay off. If you have to put it back in forward and then go back into reverse, which is common when maneuvering a trailer, the RAB often turns itself back on, so you're fighting it the whole time. If you don't shut it off you need to listen to it beep and then come grinding to a halt when the actual reverse braking kicks in. That'll get your heart pumping.

These terrible oversights and poor functional designs can easily be fixed via software upgrades if Subaru would just listen to their customers.
I think they fixed it. I just got a 2020 outback and the settings do save. You have to turn off the cross walk setting too or that can activate RAB even it’s supposed to be “off”. Both settings have saved after restart. Took some questions at the dealership today and eventually I unlocked it (fingers crossed) by asking - "is there anything that can activate the disabled RAB"?
 
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