Troubleshooting P3 Brake Controller with Electric-Over-Hydraulic Trailer Brakes

Question:

I have the new t3 hooked up in my freightliner. Im having problems with my Hydralic pump not activating all the time. When I step on the brakes the pump does not activate! If I move the t3 break controller while my foots on the brake the pump activates and voltage jumps up like I was pulling the break control knob! Im running out of patients and have pretty much troubleshooted the whole truck

asked by: Alex

Expert Reply:

I am sure you have checked this, but it sounds like your P3 brake controller may not be mounted correctly. Although the P3 can be mounted vertically from 0 to 360 degrees, the brake controller must still be pointed in the direction of travel and the front of the brake controller must be horizontal, not angled. Check out the photo that I attached from the installation instructions.

If the brake controller is mounted properly, a loose wire or connection would be the next likely culprit. First, make sure the brake controller harness is securely plugged into the back of the brake controller. Next, inspect the red wire coming from the brake controller, this should be connected to the brake switch wire that only has power when the brake pedal is pressed. This sends a signal to the brake controller when you step on the brake pedal. If that wire is loose or damaged or not securely connected, you could have the exact problem that you are describing.

Also, make sure the blue wire from the brake controller has a solid connection all the way back to the 7-way trailer connector on your Freightliner. Again, I am sure you have tested for this already since you mention you have done troubleshooting on the entire truck, but wiring problems can be very hard to find.

To make sure the brake controller is operating properly, cut the blue wire about 6 inches back from the brake controller. Use a test light to test, like part # PTW2993, for current on the blue wire when you slide the manual override on the brake controller. Because the P3 is a proportional brake controller, it will not send full voltage on the blue wire when the brake pedal is pressed if the vehicle is sitting still.

I have attached a help article on brake controller troubleshooting for you to check out.

If you are unable to find the problem or a solution, let me know what you come up with after following these steps and we can take further steps. Also, let me know how the brake controller was installed, was the brake controller hardwired to your vehicle or did you use an adapter from the vehicle manufacturer?

expert reply by: John H