I was asked to put this in a NEW posting, instead of just a "reply", so here 'tis............
Recently, we were out camping at Ft. Stevens on the Oregon coast. Getting ready to leave, got the 5'er all hooked up, ready to go. Remembered I hadn't checked the "break-away" system in a while, so decided to do that. Pulled pin, checked brakes, they were locked up, all was good.....or so I thought. Re-installed the breakaway pin, and the brakes released. We're ready to go. Started out, and as I always do, I test the trailer brakes manually with the control. GASP, no trailer brakes. Absolutely nothing. I did notice that the DIC had the message "check/service brake controller system" on it. Out to check the plug, it was OK. Check the breakaway pin, it was OK. Removed plug, re-plugged in, still nothing. Could NOT get the brakes to work. About this time, I'm mentioning to the DW that she might have to ride in the back of the rig, and if we got into an emergency, PULL THE PIN. I told her to dress warm....can you guess where THAT idea went????
Anyway, as a last resort, I pulled the trailer plug, and shut off the truck. Waited a bit, then plugged the plug back in, and started the truck back up. Lo and behold, I had brakes again.
Synopsis of event......when I pulled the breakaway pin and activated the emergency brakes on the trailer, that system utilizes the battery that is in the trailer to set the brakes. Since I had the 7 pin plug already connected to the truck (had not done that during breakaway tests before) it appears that the trailer battery "backfed" into the truck's brake control system, and "upset it's operation" characteristics. It's default was to just "shut down" operation. By removing the plug, shutting the truck off, and then restarting it and plugging back in, it "cleared" it's memory, and everything was fine after that. Had brakes all the way home, and felt much safer. Plus, DW did NOT have to ride in the back!!!
Lesson learned, at least on Chevy/GMC's with integrated brake controller...when you test the emergency break-away system, do NOT have the 7 pin plug connected! It will cause the truck's system to go into "failure mode", but at least, for me anyway, shutting the truck off and restarting, reset the system.
Lesson learned!