Electric Trailer Brakes Troubleshooting Guideby K.K. Lowell
Electric trailer brakes are a very well-engineered products. With few moving parts and no fluid to leak, they are as close to trouble free as any brake could be expected to be. For this reason, when there is an issue with electric brakes it is usually quite quick to diagnose. However most problems with these brakes are in the wiring and are not mechanical problems.
Start with the Tow Vehicle
Many times when electric brakes fail or work too abruptly, locking up the wheels with even light brake pedal pressure, the problem is in the brake controller settings. Therefore, with any electric brake problem except a noise in the brakes start by checking the controller. Watch for the controller to light up to verify that the controller has power and turns on when the brake pedal is pressed. Next, check the adjustment knobs or sliders on the controller; sometimes these are hit accidentally and become essentially turned off.
Next, the Trailer Connector
If all appears well with the controller, the next step is to check for power at the trailer connector. You will need a helper and a multimeter for this test. Have your helper depress and hold the brake pedal while you probe the connector for power. If no power is found at the connector, the problem is in the wiring between the connector and the brake controller. Check junctions in the wire back to the controller; these tend to become corroded and fail to carry current. If power is found at the controller it's time to move on to the trailer.
Problems on the Trailer
Once power is located at the trailer connector on the tow vehicle it's time to check the trailer ground. This is easier than it sounds ... with the trailer connected to the tow vehicle and the connector plugged back in, simply turn on the tow vehicle lights. If the trailer lights come on brightly, the trailer ground is good. Next, clean a spot on the frame near the axle on both sides of the trailer. Make certain to remove all rust and paint from this spot as this will be the ground connection for the multimeter during the next step. Use a small vice grip or clamp to secure the ground probe from the multimeter to this clean area. Ask your helper to press and hold the brake pedal while you probe the power wire for each brake. If power is found here when your helper is pressing down on the brake pedal but the brake still does not work, the problem is either failure of the brake electromagnet or the connection of the ground wire to the frame. Before replacing the magnet, it is a good idea to remove the ground connection from the frame, clean the terminal and frame completely and reattach the terminal to the frame. Test the brake again. If it still does not work replace the magnet. If, however, no power is found here, the issue is a corroded junction or broken wire somewhere between the brake and the trailer connector.
Brakes that Won't Release
Sometimes trailer brakes will seem to apply on their own, or won't release when the brake pedal is no longer pressed. When attempting to diagnose this condition, start with the trailer break-away switch. This switch is designed to apply the brake if the trailer should accidentally become disconnected from the tow vehicle. But on occasion the lanyard will get pulled hard enough to close the contact in the switch and apply the brakes.
Brake Noises and Mechanical Problems
Noises in the wheels of trailers equipped with electric brakes are caused by a mechanical event. To diagnose a brake noise, you must remove the wheel and tire and completely inspect the brake shoes and springs. Check for broken and missing springs and worn-out brake shoes. Inspect the magnet to make certain it is not binding or wearing unevenly.
K.K. Lowell is a freelance writer who has been writing professionally since June 2008, with articles appearing on various websites. A mechanic and truck driver for more than 40 years, Lowell is able to write knowledgeably on many automotive and mechanical subjects. He is currently pursuing a degree in English.