Troubleshooting O.L Error With a Curt Triflex Brake Controller on a 2012 Nissan Frontier

Updated 10/29/2025 | Published 03/24/2025

Question:

I recently picked up a 2024 travel trailer with my 2012 Nissan Frontier with an installed Curt Triflex brake controller. While connecting to the trailer I pulled the brake away pin to loop the cable around the frame, then replaced it in the box. I also turned the trailer battery disconnect thinking i didnt want the trailer battery drawing while towing I now know that disabled the emergency function of the brakes. I tested all functions of the 7 wire trailer electrical including brake lights. I did a pull test and the trailer brakes engaged as expected. After pulling out of the lot I heard a pop in the dash and my phone plugged into the 12v accessory port stopped charging and I noticed the brake controller started showing an O.L error. I pulled over to look at fuses and didnt find anything broken, but I also noticed the brake lights of the truck and trailer were no longer working. If I disconnect the trailer and reset the controller the O.L message goes away, then when I plug the trailer in and press the brakes it immediately goes into O.L fault. I had the dealer check the trailer brakes, and connect it to another tow vehicle and they said everything on the trailer end tests good. Any ideas?

asked by: Joel F

Expert Reply:

Hey Joel, so from what I can see an O.L error is an "overloaded" error which means the brake controller is detecting a fault in the trailer wiring.

Since you already checked the trailer side, I'd move to the vehicle side if you haven't already. I'd start by checking fuses and make sure nothing is blown, then move to the wiring that goes to the controller and check for breaks, frays, or damaged wire. Any of those things can created a short and might be the reason for the error.

If the wiring looks fine, I'd check the grounds as well. You'll want to make sure the grounds are connected to a good source and that they are not loose.

If all that checks fine, the there could be an issue with the controller and would need to be replaced.

If you have any other questions, please feel free to let me know!

expert reply by: Bryce D

Lazer S.

10/27/2025

Hey Joel, how did things go after checking the wiring and grounds on your Frontier and the Curt Triflex controller? Were you able to track down what caused the O.L error? Your update could make it easier for others troubleshooting the same issue.

Joel F.

10/27/2025

@LazerS Hello Lazer, yes here is the update as best as I have been able to diagnose with several mechanics: The initial cause of the failure was the brake controller itself, I had it set to almost the highest gain which was needed for an older trailer I had been hauling with very worn down brakes. I did not turn the gain down when i hooked up to the new trailer. It seems the new brakes combined with the high gain setting caused an overload and cased a short in the controller when I engaged the test lever at full to test the brakes. After testing I had embarked on the road and the damage was already done, the short in the controller sent an overload through the brake control system of the vehicle and broke a fuze in the brake system which caused the ECM computer to read a fault and engaged "limp mode" on my tow vehicle. The short in the controller continued to send 12v across the PCB in the controller and it quickly overheated and several components popped. The broken fuse did not completely break however, and the filament re-fused making it very difficult to track down, it was barely visible in the fuse assembly until it was taken out and inspected very closely. Once I disconnected the trailer and the brake controller, the ECM cleared the fault and my truck went back into normal operation. I replaced the brake controller, and the fuze, and everything has been good since.

Lazer S.

10/29/2025

@JoelF Holy cow! I can't say I have heard of a brake controller causing this many problems, but I'm glad to hear it all got sorted out. Did you go with a different brake controller for the replacement?