First off, thank you for everyone who has contributed in years past. It's all been really helpful!
Second, sorry for resurrecting a 10-year-old thread.
I'm curious what the OP ultimately ended up with. I have a 2003 E53 (X5) 4.4 that has had the three amber lights come on intermittently. It's been happening for awhile, and while I feel very close to a solution, it's still somewhat a mystery. A couple of notes before the specific ABS/DSC/Brake issue: My power steering reservoir and coolant reservoir have both had leaks right onto the main connector. I've recently dried and cleaned the connector, as well as applied dielectric grease into each hole. Also it sounds like my U joint or something in the neighborhood is wearing out. At times, when the 3 lights come on, it will cause the rear brakes to completely lock up. It doesn't put the vehicle to a screeching halt but instead creates a pretty severe brake drag to the point the rotors heat up red. I've just replaced those rear rotors, brake pads and both brake wear sensors.
As for this issue, INPA is consistently indicating the same errors as the OP. Here's the interesting part (for me at least): when watching the live data, both the pressure sensor and the brake switch lights fluctuate constantly until I press the pedal. Then they seem to act normally from what I've seen so far. Does this mean the brake light switch may be the culprit... or something else? Here's what I'm down to (I believe):
* bad brake light switch
* dirty/bad speed sensor(s)
* bad ABS control module
* bad DSC pressure sensor