I'm not really sure about the '99 E430, but assuming that the technology is about the same-----I have a 1988 300 SE that did the same thing. The fix was as simple as cleaning the sensors at the rotor hub and the corresponding gaps cast into the hub. The sensors "read" those gaps and if they are full of mud or whatever, they don't read correctly and thus the "LIGHT" on the dash. It was a VERY cheap fix. That's not gospel or nuthin'--jist my experience........