P3 Trailer Brake Controller is Getting Power from Battery and Stop Light Switch But No Voltage Out

Question:

Brakes not working on caravan. Trouble shooting diagnostic shows. battery voltage 14.06 volts stoplight without brake on .04 volts stoplight with brake on 13.5 volts. output voltage o.o output current 0.0 Where should I start looking for problem?

asked by: Bevis

Expert Reply:

It looks like your P3 brake controller, # 90195, is getting power from the battery and power from the brake switch when the brake pedal is pressed so that is good. But it is not sending power along the blue wire. Do the same test but instead of the brake pedal use the manual override and make sure that the output power is set to the maximum. It should show around 12 volts output.

If it says 0.0 again then use a circuit tester such as # PTW2993 or a multimeter, # PT89ZR. Sever the blue wire several inches back from the controller. Test the end coming out of the controller while fully applying the manual override. If it does not show power with the manual override pressed, then there is something wrong inside the controller and it will need to be replaced.

If it does have the proper power but still tells you 0.0 then there is some other internal error, and you will want to replace the controller.

If this happens to be happening on a Chevy or GMC truck or SUV then it is possible that it is not sending power back because it thinks a trailer is not connected. On some GM vehicles, the wire is not run for brake output all the way to the back of the vehicle.

I have included some links that will help troubleshoot further.