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I’ve been towing with the Tekonsha P3 brake controller for roughly 8,000 miles now. The first half of that with minimal issues, but for the last half the brake controller intermittently flashes a bright red warning sign that reads “Output Shorted - No Brakes.” Its an overload warning that is shown in the operating manual.

This happens intermittently when braking, and is somewhat scary especially on descents when I can tell the trailer brakes aren’t engaged. Fortunately a quick release of the brake pedal and depressing again usually does the trick and they re-engage. The other odd thing is that it will also flash the warning sporadically when simply cruising along and not depressing the brakes. It’ll flash the warning for a quick second or two then go away. This happens without fail every time I tow our travel trailer now. I have only towed the same travel trailer so can’t say I’ve seen the same thing happen with multiple tow objects.

I had the vehicle wiring looked at by Subaru and they said all looked fine. I had the RV pretty thoroughly inspected and they said all looked fine (didn’t take apart the wheels and drums to look at the magnets though), and called Tekonsha and they told me it wasn’t a brake controller issue since the warning isn’t occurring when the controller is on and no trailer is hooked up. They said based on that it must be a connection in the vehicle or trailer.

I’ll add that my Ascent has seemed to have some electrical issues so far along the way. Had the trailer fuse blow one time and that’s been replaced. Also had a large slow burning fuse under the main hood go out that was noticed when the brake controller wouldn’t power on. Both have been replaced but seem to have been rather unique experiences and odd issues.

Based on all the above, I’m kind of out of thoughts and this forum has been tremendously helpful in the past. Any thoughts?? Thanks!
 

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2020 Ascent Touring
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I have the port installed OEM hitch and wiring. Assuming your's is OEM since you had Subaru check connections. Having read the hitch installation manual and the descriptions from the diyers, the wiring that goes through a body grommet is a tight path. I'd look there to see if any insulation has been damaged. Vibrations, tight bends around sheet metal can eventually dig through insulation. I'd also get a look at the brake drum wiring for the same thing.

Good luck.
 

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I’ve been towing with the Tekonsha P3 brake controller for roughly 8,000 miles now. The first half of that with minimal issues, but for the last half the brake controller intermittently flashes a bright red warning sign that reads “Output Shorted - No Brakes.” Its an overload warning that is shown in the operating manual.

This happens intermittently when braking, and is somewhat scary especially on descents when I can tell the trailer brakes aren’t engaged. Fortunately a quick release of the brake pedal and depressing again usually does the trick and they re-engage. The other odd thing is that it will also flash the warning sporadically when simply cruising along and not depressing the brakes. It’ll flash the warning for a quick second or two then go away. This happens without fail every time I tow our travel trailer now. I have only towed the same travel trailer so can’t say I’ve seen the same thing happen with multiple tow objects.

I had the vehicle wiring looked at by Subaru and they said all looked fine. I had the RV pretty thoroughly inspected and they said all looked fine (didn’t take apart the wheels and drums to look at the magnets though), and called Tekonsha and they told me it wasn’t a brake controller issue since the warning isn’t occurring when the controller is on and no trailer is hooked up. They said based on that it must be a connection in the vehicle or trailer.

I’ll add that my Ascent has seemed to have some electrical issues so far along the way. Had the trailer fuse blow one time and that’s been replaced. Also had a large slow burning fuse under the main hood go out that was noticed when the brake controller wouldn’t power on. Both have been replaced but seem to have been rather unique experiences and odd issues.

Based on all the above, I’m kind of out of thoughts and this forum has been tremendously helpful in the past. Any thoughts?? Thanks!
I would review the ladder diagram and check relays.
 
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