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Troubleshooting 3.6V Power on Brake Controller Circuit of 2011 GMC Yukon XL


customer brought in trailer and vehicle with Brake Rite system. i have repaired regular electric but never seen this style. the brake blue wire only has 3.6 volts with brakes applied or not applied. i can put power to wire withe power probe and electric moter on trailer comes on. he said it was working until someone rewired it . it looks correct when looking at wiring diagram on line . thanks


Expert Reply:

It sounds like you are saying the brake circuit on the 2011 GMC Yukon XL (5 o'clock pin on vehicle 7-Way) has constant 3.6V no matter if the brake pedal or manual override on the brake controller is used or not. Start off by disconnecting the Yukon from the trailer and then testing the pin for the brake controller circuit with a circuit tester like # PTW2992 to see if there is constant power on the trailer side (could be backfeed from breakaway battery) or the vehicle side.

If there is power on the trailer side of things then it could be that the BrakeRite # T4813100 has a bad circuit board and the entire unit needs to be replaced.

If you have constant power on the Yukon side then disconnect the brake controller and see if that makes a difference. If it doesn't then the wiring on the vehicle needs to be inspected. If it does make a difference then disconnect the brake controller and test the wiring going into the brake controller. Only one wire (or pin) that connects to the controller should have constant 12V power. If this checks out and you don't have that 3.6V power with the brake controller disconnected then the controller needs to be replaced. Otherwise some wiring is brackfeeding or crossing over somewhere and it's just a matter of tracing and testing to track it down.

expert reply by:
Jon G

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