now this is what I like ! this is all very good info for those that don't understand. when I was in the transportation business we would test the braking rates also change the brake pad material and tweak brake pressures for better brake control . the reason for this is if you start to slip/slip then the ABS gets activated by the computer/PCM and you loose in you braking distance which is not good. ever see what those BMW brake rotors look like ? pure brake control. the bigger the rotors/calipers the greater the brake effort and control. - - - Updated - - - the ECBM electronic control brake module gets tested by the programed control module PCM at every start. on many of our vehicles the relay contacts get burned up and then you get the ABS light to come on with just starting the vehicle and never even braking or moving the shift lever from park. the PCM receives the speed signals from the tranny and the front axles. then with the programing decides how it is going to act/control the vehicles failure indicators/brake components. when you get a slide condition the pulsing is from the ABS pump and valve dump/apply of brake pressure as you keep your foot pushing down on the brake. when the speed frequencies all agree then the power to the ECBM from the PCM is shutdown to condition normal. what I seen happen is these ABS valves can get stuck in the open no pressure position then you cannot stop. very scary . this can occur if you push back the back caliper pistons with the bleed screw closed . then all the dirty brake fluid fouls up the ABS valves in the control unit. GM last I checked does not have a brake fluid replacement cycle . this is not good . most manufacturers of high priced quality performance vehicles do have a replacement period for these fluids.I have replaced my fluid 3X since 2000. this may be why my brakes still work very good even when towing.