The AC4400CW in general seems kinda buggy. Disappointing because it's part of the reason I bought the game. Hopefully fixed soon!
The brakes seem to be stuck on about 50% of the time. It won't go over 20kmph even on a small grade pulling just regular autoracks. The BP should be 0 when I release all the brakes but sometimes it stays at 30 as if I got half the brakes on. The tutorial can't even be completed because you can't enter the screen mode.
I have a funny feeling that you may have the brakes in trail mode. On the computer screen, go into air, and turn the brakes into "lead". Make sure to press save on the computer screen. I hope that fixes your problem. -Dean
I got the same impression, although I didn't see any air pressure registering. It could be your MU configuration with the trail loco? Maybe only the leading loco was working properly.