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Trailer Brakes Locked Up, Brake Controller Blue Wire Shows Constant 14 Volts


Hello, I am driving a 2001 Nissan Pathfinder and using the Primus IQ Controller. I was pulling my newer travel trailer this weekend and was going about 5 mph in a campground when all of a sudden the trailer brakes locked up I was not pressing the brake pedal and would not unlock unless the trailer was disconnected from the tow vehicle. Was forced to pull trailer home with another vehicle and it towed perfectly with the brakes working well. I have towed 1000s of miles with the Pathfinder and controller and until now had zero issues. I have tried trouble shooting this and this is what I have found so far. Installed a different controller and am having the same issue. With the controller disconnected, the 4 pin connector exposed at the controller connection point, I am getting 14.2V from the black wire, 14.2V from the blue wire, and 0V from the red wire whether the brake pedal is pressed or not. I am really at a loss on this. Like I said it has worked for years and 3 trips towing the current trailer and all of a sudden the sudden failure and the brakes locking up. One other strange thing that I have noticed is that I typically run in B1 mode with a boost of 48, after the lock up event with the trailer connected, the boost will only run up to 14 and no higher. This may be due to the fact that the trailer brakes are already locked but weird. Please help. I have also checked fuse and cannot find anything.


Helpful Expert Reply:

It sounds like there is an internal issue with the controller and/or a short on the brake output wire. The easiest thing to check would be the vehicle side trailer connector. Corrosion can cause a short causing constant power draw on the blue wire. Make sure the connector is clean and free of corrosion inside where the wires attach and outside on the pins.

You can also inspect the wiring as far as you can under the Pathfinder. Check for damaged wires with copper touching bare metal.

To test the brake controller you will need to sever the blue wire several inches from the back of the controller. Then use your circuit tester such to test the end of the blue wire coming out of the controller. It should only have power when you apply the manual override. If it shows power at idle then there is something wrong with the controller and it will need to be replaced.

If it tests fine then reconnect the blue wire. You can test the brake output pin at the back of the truck and it should only show power with the manual override. If it shows power any other time then there is a short somewhere between the connector and the brake controller you will need to track down.

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