Troubleshooting Prodigy P3 Brake Controller Not Showing Voltage Increase with Brake Pedal

Updated 04/08/2021 | Published 04/07/2021

Question:

I am out of ideas on where to turn to next... wired a Tekonsha P3 into our 2013 Tiffin Allegro Bus. Previous owners appeared to have had a Roadmaster system set up, and they really butchered some wires - both under the dash, and at the rear 7 way, but that’s a different story. When connected to the trailer, I have all lights and signals on the trailer, but the P3 shows trailer disconnected. I used a circuit tester on all positions of the 7 way and everything is receiving power. The blue brake wire in the 5 o’clock position tests with power, as I suspected that was the initial fault as it wasn’t even connected initially. Trailer connects just fine to another vehicle and that vehicles integrated brake controller Ford Expedition shows connected and the manual override locks up the brakes. Troubleshooting on the P3 and it shows power at 13.9v. Next it shows stoplight at 0.0 while at idle, and 13.9 when brake pedal depressed. Output voltage at 2.2 when at idle, and 0 when brake pedal depressed. Output current stays at 0.0 even when brake pedal depressed. I’m stumped.

asked by: Davey D

Helpful Expert Reply:

Are you testing the voltage when the vehicle is at a stand still? If so you should note that since the controller is proportional it needs to feel a change in inertia to send out a voltage increase. If you haven't tested to see if the trailer brakes are actually applying you might but you'll have to be moving. Does the manual override lever increase the voltage or change anything at all when applied?

You might check the position of the controller as well since the sensor requires it to be positioned in a certain way to activate. It needs to face squarely towards the rear of the vehicle and be level from side to side as well.

expert reply by: Jameson C