Why Would Prodigy P3 Brake Controller Show Varying Voltage at all Times As Output

Updated 05/25/2025 | Published 04/08/2025

Question:

I installed a Tekonsha Prodigy P3 Trailer Brake Controller with proportional breaking late last year and noticed that the proportional breaking may not be working correctly. The amount of brake applied while slowing is inconsistent and bounces around. In the troubleshooting menu, all looks normal except for the Output voltage. It bounces around as well, even when sitting completely still. It is mounted straight with the truck. If I tilt it up and down the output bolts jolt around but still inconsistently. Looking for any ideas, or perhaps whether I could have ended up with a faulty unit.

asked by: Austin

Expert Reply:

Hey Austin, it sounds like your P3 part # 90195 has a short from the 12 volt power wire (black) to the stoplight switch (red) and the brake controller thinks that you are applying the brakes and is activating the controller which is making it think it needs to search for braking action. I would go over the red and black wire of the brake controller and see if you can find any cut or exposed wire and insulate as needed with electrical tape.

expert reply by: Jameson C

Austin

4/9/2025

Hi there! Thanks for the reply. This is actually only occurring WHILE I’m pressing the brakes. Without the brake pedal pressed it is a constant 0.0 volts. Once brakes are applied, the voltage starts around .8, then jumps to 1.6 and up and down from there. If I angle the unit up and down to simulated proportion, the output power jumps sporadically in whatever direction I’m angling it. If I angle it up, the output power jumps high. If I angle it down it jumps in the lower range but the changes are never fluid, always bouncing around. When I’ve performed any of these tests, it is always while the brakes are pressed.

Jameson C.

4/9/2025

@Austin Have you tried a hard reset by unplugging the controller and plugging back in? Sometimes that takes care of quirks like that.

Austin

5/24/2025

@JamesonC I did what you suggested and it did seem to stabilize the output power while I’m holding the brake pedal. However, while I’m pulling a trailer and braking the amount of braking power applied still seems to be “jumpy” seems like with every wiggle the truck makes the brakes get applied sporadically. Is that just normal for this kind of controller and the bumps around and impacts the progressive braking?

Jameson C.

5/25/2025

@Austin A proportional controller can fluctuate a bit with bumps when braking since the sensor can misinterpret the bump as additional braking but it shouldn't be too bad. Is the brake controller sitting level from side to side and also facing squarely towards the rear of the vehicle? If those two things aren't within the acceptable range the braking output will be unpredictable.