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Discussion Starter · #1 ·
Hello all this is my first time posting to this forum. Just got our OEM trailer hitch installed by the dealer on a '19 Ascent Limited - searched pretty deep and have not found someone else with this problem.

I am installing the P3 brake controller today. Got everything mounted and wired up, plugged the harness to the factory plug under the drive side dash near the kick panel. No power. P3 controller will not turn on.
  • Checked power to the plug with a volt meter starting at the plug to the P3 controller and worked down each connection point all the way to the factory female plug end itself.
  • There seems to be no power at the factory plug.
  • Checked the fuse in the passenger compartment fuse panel (#28) and it is good.
  • Checked power to the positive side of the fuse terminal, 12+ volts
I am stumped. Perhaps I am looking at the wrong fuse? Owners manual lists #28 at "Trail" I assume this is short for trailer. Any help would be greatly appreciated.

Also, big thanks to everyone on this forum. Even though I am a new member and have not posted before, all the previous posts have been VERY helpful.
 

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Hello all this is my first time posting to this forum. Just got our OEM trailer hitch installed by the dealer on a '19 Ascent Limited - searched pretty deep and have not found someone else with this problem.

I am installing the P3 brake controller today. Got everything mounted and wired up, plugged the harness to the factory plug under the drive side dash near the kick panel. No power. P3 controller will not turn on.
  • Checked power to the plug with a volt meter starting at the plug to the P3 controller and worked down each connection point all the way to the factory female plug end itself.
  • There seems to be no power at the factory plug.
  • Checked the fuse in the passenger compartment fuse panel (#28) and it is good.
  • Checked power to the positive side of the fuse terminal, 12+ volts
I am stumped. Perhaps I am looking at the wrong fuse? Owners manual lists #28 at "Trail" I assume this is short for trailer. Any help would be greatly appreciated.

Also, big thanks to everyone on this forum. Even though I am a new member and have not posted before, all the previous posts have been VERY helpful.
I have the exact same controller - two questions. First, is the connector on the controller itself fully seated? And when you tested for power was the ignition in the "on" position?
 

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Discussion Starter · #3 ·
I have the exact same controller - two questions. First, is the connector on the controller itself fully seated? And when you tested for power was the ignition in the "on" position?
Yes, the ignition is on and the plug is completely seated. I tested volts to the factory installed female plug under the dash and get nothing. Seems like a fuse issue but fuses look good.

Guess I'm trying to make sure there is not a fuse somewhere I am not aware of or I may be checking the wrong fuse.
 

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I could be totally out to lunch on this, but I recall seeing a post that said a trailer needs to be connected for the brake controller circuitry to switch on.
 

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I could be totally out to lunch on this, but I recall seeing a post that said a trailer needs to be connected for the brake controller circuitry to switch on.
The Tekonsha Prodigy will light up without a trailer connected, with the display showing "No Trailer Connected," or words to that effect.
 

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Discussion Starter · #6 ·
The Tekonsha Prodigy will light up without a trailer connected, with the display showing "No Trailer Connected," or words to that effect.
I could see how that would make sense though. Gave it a try and sadly still no power. Going to have to take it back to the dealer this week and see what they can figure out. It is definitely not an issue with the P3 or harness, something on the factory side.
 

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Since the dealer installed the towing equipment....I'd be right back there to get them to make the wiring work as expected. :)
 

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Discussion Starter · #8 ·
Quick update on the trailer brake saga. After two more trips to the dealer they insist there is power to the factory plug under the dash and that the problem is with the brake controller. I'm no stranger to auto mechanics and electronics, I tested the plug after each trip and get no power to the battery terminal. I also temporarily connected the P3 to a 12v source and it fired right up so I know it is not the P3.

I had a very blunt conversation with the dealer about the likely hood of my future business with them (spoiler alert, there will be none!)

So for now I am researching this forum, I remember seeing someone had powered their unit from the USB in the cubby below the radio - going to go that route as a temp solution until i can get the Ascent into a different dealer.
 

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Why don't you just go to a different Subaru dealer's service department to get this diagnosed and fixed?
 
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Today when I hooked up my P3 to my power cord I keep tucked up under the dash there was no power to the P3. I normally don't leave it connected, only mounting it when I tow, which Ive done successfully for almost two years, and as recently as last week on a four day camping trip. Placed the P3 in a friend's truck who has the P2, and it lit right up, so it's not the controller. Removed the harness at the Subaru supplied connector to the left of my foot, and redid all four connections between the Subaru supplied pigtail and the Tekonsha harness (this was after first replacing both the 20 amp inline fuse that came with the Tekonsha harness, as well as the 15 amp mini fuse identified as "Trail"), all to no avail. A multimeter shows no power to the connector that goes into the controller. I wonder if there is another fuse inline leading to the Subaru male plug by my left foot?
 

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Discussion Starter · #11 ·
Today when I hooked up my P3 to my power cord I keep tucked up under the dash there was no power to the P3. I normally don't leave it connected, only mounting it when I tow, which Ive done successfully for almost two years, and as recently as last week on a four day camping trip. Placed the P3 in a friend's truck who has the P2, and it lit right up, so it's not the controller. Removed the harness at the Subaru supplied connector to the left of my foot, and redid all four connections between the Subaru supplied pigtail and the Tekonsha harness (this was after first replacing both the 20 amp inline fuse that came with the Tekonsha harness, as well as the 15 amp mini fuse identified as "Trail"), all to no avail. A multimeter shows no power to the connector that goes into the controller. I wonder if there is another fuse inline leading to the Subaru male plug by my left foot?
This was my thought as well but I have not been able to locate another fuse. I did make an appointment at another subaru dealer to try to get this resolved next Tuesday. We have a big trip upcoming next Friday, 7/10 hence my urgency to get this resolved. It seems like it must be an inline fuse somewhere.
 

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This was my thought as well but I have not been able to locate another fuse. I did make an appointment at another subaru dealer to try to get this resolved next Tuesday. We have a big trip upcoming next Friday, 7/10 hence my urgency to get this resolved. It seems like it must be an inline fuse somewhere.
I have an appointment early Tuesday as well. I've ordered from eTrailer the Ascent specific wiring harness to replace my current one, though I don't believe that's the issue. My service manager has been a great help for five years, so I'm hoping that they can identify the issue quickly, though it won't be in time for my fly fishing trip 6-10 July that's now a bust.
 

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This was my thought as well but I have not been able to locate another fuse. I did make an appointment at another subaru dealer to try to get this resolved next Tuesday. We have a big trip upcoming next Friday, 7/10 hence my urgency to get this resolved. It seems like it must be an inline fuse somewhere.
The short answer is it was a fuse located in the fuse compartment in the engine bay. It's an odd-shaped 40 amp fuse, which the tech referred to as a slow-burn fuse. The parts department didn't have one on hand, but the tech had one "lying around" from another vehicle and used it. I've attached two photos, one of page 490 in my manual that shows the blank space that the fuse sits in, but the manual in no way identifies, and the second photo shows the inside of the fuse cover and the diagram that identifies it as (40A) (SBF 4). They could not explain why they thought it failed, but they did point out that the black positive connector on the Tekonsha wiring harness that plugs into the back of the controller is scorched. I do not have my brake controller permanently mounted, so maybe when I connected it last Friday, or removed it from my last trip four days prior, I attached or removed it just right to cause this scorching and the fuse to fail, but who knows. I would have thought the inline 20 amp fuse would have failed first, but I slept through electronics classes in school. I also had them order me one of these unique fuses as I don't think they're hanging on the rack at the auto parts store (unlike the other blade-type fuses used in the car) to have along as a spare, and I might just go ahead and permanently mount my brake controller as well and leave it always connected..
 

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Discussion Starter · #14 ·
The short answer is it was a fuse located in the fuse compartment in the engine bay. It's an odd-shaped 40 amp fuse, which the tech referred to as a slow-burn fuse. The parts department didn't have one on hand, but the tech had one "lying around" from another vehicle and used it. I've attached two photos, one of page 490 in my manual that shows the blank space that the fuse sits in, but the manual in no way identifies, and the second photo shows the inside of the fuse cover and the diagram that identifies it as (40A) (SBF 4). They could not explain why they thought it failed, but they did point out that the black positive connector on the Tekonsha wiring harness that plugs into the back of the controller is scorched. I do not have my brake controller permanently mounted, so maybe when I connected it last Friday, or removed it from my last trip four days prior, I attached or removed it just right to cause this scorching and the fuse to fail, but who knows. I would have thought the inline 20 amp fuse would have failed first, but I slept through electronics classes in school. I also had them order me one of these unique fuses as I don't think they're hanging on the rack at the auto parts store (unlike the other blade-type fuses used in the car) to have along as a spare, and I might just go ahead and permanently mount my brake controller as well and leave it always connected..
Thanks so much for the post and the photos. I just got the same news from my dealer but I didn't get pictures of the exact location. Glad that we finally have it figured out so future Ascent owners can fix the issue without a visit to the dealer. I knew it had to be an unmarked fuse somewhere.
 

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Thanks so much for the post and the photos. I just got the same news from my dealer but I didn't get pictures of the exact location. Glad that we finally have it figured out so future Ascent owners can fix the issue without a visit to the dealer. I knew it had to be an unmarked fuse somewhere.
Just had the same issue occur to me last week and this post helped me diagnose and fix - thank you! I did find this 40 amp fuse at the local auto parts store luckily (CarQuest), but it was the only one they had of the sort. I’ll be ordering some spares to have on hand.

I would love to know what caused the issue to prevent it from happening again, but sounds like no service department has been able to get that far. I also had my brake controller unplugged for the past month or so, and went to go plug it back in to no avail. I had hooked up the trailer connector in the back before attempting to plug in the controller, so I wonder if that somehow caused the short and fuse to blow? I’m certainly no electrical expert, so that’s just a guess, but all I could think of...considering the fuse either blew then or between towing when no controller was hooked up to it...

Any idea what this fuse is used for besides powering the brake controller, or is that it’s only purpose?
 
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