Troubleshooting P3 Showing Braking Voltage When Pedal is Not Pressed

Question:

I upgraded to a P3 brake controller and noticed output when the pedal was not pressed. I went into troubleshooting and sure enough it show stoplight voltage. I can do a quick tap on the pedal and it resets and is fine. I put a multimeter on the connector with the P3 removed and the voltage is coming from my truck. The brake light function normally its just the factory installed wire for a brake controller thats under the dash that is showing voltage. Again a quick tap to send voltage appears to reset. I have no idea how long this is happening or if it just started as I upgraded from a Voyager brake controller and did not have the output display or diagnostics. Could this be a relay issue or can you point me in a direction? The truck is a 2008 Chevy 3500 w/a Duramax. Thanks for your time.

asked by: Joe C

Expert Reply:

When you removed the P3 # 90195 brake controller and found the same voltage coming from your truck, it leads me to believe that you either have a short in your system or the brake light signal is not functioning correctly. I recommend putting a circuit tester like # PTW2993 on the cold side of your stop light switch and seeing if you have signal. If so, your stoplight switch may need to be replaced. Your quick tap on the brakes resetting it leads me to believe that your switch may be sticking or going bad.

Another possible cause of this would be if your trailer brake magnets are going bad. I've attached an article to assist in testing them.

If you need further help, let me know and we can continue to troubleshoot.

expert reply by: Jason S