Last year I had an issue where the brakes would come on all by themselves (only below 20°), causing me to pull over and not let me go anywhere. I thought it was water so I would turn my truck off, drain the tanks, and the lights (outside) would turn off until I built full pressure (which took forever). I took it to Peterbilt (2016 Peterbilt 587) in which they diagnosed the problem as a brake switch (not the problem). I spent $2200 for this repair (in which I thought was fixed) and I didn't have any problems as it was warming up since winter had passed. Well, this winter the same thing happened but at least I knew a work around to get me to a shop safely (drain tanks, start truck, and hold protection valves pushed in, and go before pressure builds up). I couldn't find ANYTHING about it online given the symptoms (outside brake lights illuminated, front brakes locked, only below 20°, brakes unlocked after draining tanks). I even tried alcohol in the tanks; didn't work. Was told it could also be brake pedal plunger not sliding back into place, tractor/trailer protection valves, or abs valve clogged, or even adaptive cruise sensor fault. Took it to a TA in Cheyenne where they knew what was wrong. It was the air dryer filter; full of water; frozen. $200 filter and I was on my way with a symptoms-free truck in single digits temperature. Hopefully this finds it's way to someone else with the same problems and can spare them the agony of throwing parts at it to fix.