horn beeps after shutoff.

Sorry man, I don't know what else to tell you. Your truck all computer controlled. The horn will beep because the body controller is getting a signal to tell it to beep. If the body controller is not seeing a valid park brake signal, even though you are physically setting them, this would cause this issue. If the body controller is not seeing a park brake signal, your park brake warning light would be missing in the dash. If you have remote locks with the horn panic button, perhaps there is some radio interference with some other electronic devices. Maybe the button is making slight contact due to the way you hold it... I can guess all day. You are going to have to get some one with a laptop and Diamond Logic builder software to monitor the Body Controller inputs when you key off and walk away and try to duplicate the issue and troubleshoot from there. Aside from unplugging the horn there is no secret hidden switch that will make the problem go away. One way or another, this is a tricky problem that I have never heard of, and you're looking at a trip to the shop. There is a know issue with defective horn pads that go off at random, but that is with buses and medium trucks built after March of 2010 to Feb 2012. This problem only seems to occur in low temps before the cab is warmed up.

 

I got the same trouble on this 2010

 

I wish people would come back here after they found the problem to report back what they found and actually try to be part of this forum community and not be someone who is just too cheap to take it to a shop.

 

Im looking in to it I can stop it some times while pushing the switch on the door .
while it's open tracking down the problem.

 

It’s the brakes. Just had it happen, came here, then confirmed.

 

Let me elaborate I’ve experienced the issue before and just recently the other day. I came here to look for answers, read this thread, then went to confirm that I could reproduce the issue. So it is confirmed for my 15 pornstar that NOT popping the brakes before I killed the truck or perhaps popping them too fast then turning the truck off is what reproduced the honking for me.