Trailer Brakes Stopped Working with P3 Brake Controller in a 2012 Ford Expedition

Question:

Prodigy P3 Controller / 2012 Expedition. Controller shows voltage output, but when pressing the controller manual lever or pressing brake pedal, trailer brakes do not work. Brakes worked about 3 weeks ago just fine. Any suggestions? Thanks....

asked by: Phil

Expert Reply:

With your trailer connected your P3 brake controller # 90195 should show 0.0 with a picture of a truck and traielr when the trailer is connected. If it does not, then the controller is not sensing the trailer. If that is the case, you would not have any trailer brakes.

It is also possible that the trailer brakes need to be adjusted to move the shoes closer to the insides of the drums. When adjusted properly you should hear a slight but constant drag of the pads on the drum. Using a brake adjustment tool, # W80630, makes adjusting the brakes easier.

You can also do some testing to determine if the brake controller is the problem. Perform these tests with NO trailer connected. In the truck cab you will need to sever the blue wire several inches from the back of the controller. Then use a circuit tester such as # PTW2993 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. Then move on to the truck side trailer connector. Many times, dirt or corrosion can cause a short in a trailer connector. Make sure the truck and the trailer side connectors are clean and free of corrosion inside and out.

You can test the brake output pin 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.

If the truck side checks out fine, then it could be the wiring to the brake magnets or the magnets themselves. Inspect the power wires to the magnets and look for pinched, frayed, or damaged wires and fix as needed. Make sure the ground wires are attached to clean and corrosion free bare metal surfaces.

You can visually inspect the magnets and if you can see the copper windings coming through the magnets will need to be replaced. To further test the magnets, you can follow the help article I have linked. I have also included some help articles on testing and troubleshooting brake controllers for you.