Did I Fry My Tekonsha P3 Brake Controller? Would Not Power on Until Unplugged and Held Override.

Updated 09/03/2025 | Published 08/04/2025

Question:

Controller has no brake output. All light functions work including brake. But I can max out the controller and only get .5 of a volt going to the trailer. My other truck with a different controller has no issues on same trailer. Note. Had a booster pack on a dump trailer battery. Truck was turned off but trailer was connected. Could this have “fried the controller”. The controller would not power up till I unplugged it and held the manual override over. Also every no and then when. Only when trailer is disconnected it will read short to battery

asked by: Tye R

Tekonsha Brake Controller
(click to enlarge)

Expert Reply:

Hello Tye,

I am sorry to hear that you are having issues with your Tekonsha Prodigy P3 Trailer Brake Controller # 90195. Thank you for the detailed information, and it was smart to hook up a different truck so we can eliminate the trailer being the issue.

Even though the truck was turned off, having the trailer connected while a booster pack was powering the trailer battery can cause a voltage spike to travel back up the 12V auxiliary line into your controller. Many brake controllers are sensitive to irregular voltage. A booster pack, especially when first connected or under load, can spike the voltage to well above 14–15 volts, and if that back feeds into your truck’s brake controller, it can damage the internal circuitry. That would explain why you’re now only getting about 0.5 volts of brake output, even when maxing the settings, and why you had to unplug it and use the manual override just to get it to power back on. It is kind of like how if the breakaway is pulled on the trailer with the vehicle connected, the high voltage goes back to the controller and fries it.

Also, the “short to battery” message you're seeing when the trailer isn’t even plugged in is another red flag, that’s not normal behavior. It often points to an internal short or a logic error inside the controller itself. That kind of message without any load present usually means something inside the controller isn’t working properly anymore.

To confirm it, you could do a couple of quick checks with a multimeter like # PT89ZR. First, unplug the trailer and test the blue brake output wire coming from the back of the controller (or wherever it’s accessible). Then, use the manual override and see what kind of voltage you’re getting. If it’s still around 0.5 volts at full override, the controller is the issue. You mentioned you used a different truck and brake controller to find out that the trailer is fine, is there anyway you could put that brake controller in this truck to make sure that it is not a vehicle wiring issue?

Last but not least, check the grounds, make sure they have a good clean connection. Unfortunately, it sounds like you are going to need a new controller for this truck. What is the year, make, and model?

expert reply by: Kate F

Kate F.

9/2/2025

Hey Tye, Did you have a chance to test the voltage with a multimeter to confirm if the controller is the issue? I'm asking because your experience could help others who might face a similar situation.

Tye R.

9/2/2025

@KateF I have not had a chance yet to test. But full override still has no brake output. But if I change the angle of the controller it will jump to 13 volt output. Then go back to just doing .5 of a volt. I’ll see if it can be swapped to my other truck. Its currently in a 2005 Chevy 2500

Kate F.

9/3/2025

@TyeR Sure thing! The Tekonsha P3 is pretty forgiving, but it does need to be mounted solidly so it can “feel” the motion of your truck. You can swivel it side-to-side as much as you want, but vertically it needs to stay within about 70° up or down from level. If it’s too far off or loose, the sensor inside can get confused and cause weird voltage readings, so just make sure it’s snug, not wobbly, and angled within that range and you’ll be good to go. Let me know how it works in the other truck when you get the chance to swap it out.