I have a Roadtrek RV on a 2017 Dodge Ram Promaster 3500 chassis. I was driving down a steep grade (7%) with tow haul engaged. Going about 50 mph, I braked for 2-3 seconds and then saw a warning message on the dash (something about system hydraulic... sorry, can't remember the exact verbiage) and the "brake hydraulic system red warning light" came on and stayed solid. Turned off the tow haul after I got to the bottom of the mountain and continued driving. Didn't have any problem braking, but the warning light remained solid the whole time. After driving a bit longer, I stopped and turned off the vehicle. When I started it back up, the "brake hydraulic system red warning light" did not illuminate. It seemed like things got "reset" somehow when I turned off the vehicle? Any idea why the warning light would have come on in the first place? Can you not manually brake when tow haul is engaged?