My M2 ABS modulator valve was replaced because it was leaking air out of the bottom area (after 860,000 mi.s) causing the air pump to cycle more then it should, found it by spraying soapy water on all the air components and connections. ABS Mod valve was around $300 and installed myself.
Also, ABS wheel sensors are close tolerance to the hub ring, directions for install say there should be no space between the two, but upto .015 inches is OK. These sensors are not easy to move in and out for this adjustment and one can easily damage the sensor trying to pry it in or out while mounted. The wheel bearing issue would make sense. Me thinks techs don't take the time to get the sensors set correctly, it took me about 30 minutes each side to set them at .010 with a feeler gauge. To replace them without removing the hub, you have to remove two large bolts holding the sensor housing on and takes a few tries to get the tolerance correct. No ABS light now.
As far as DOT regs, and don't have time to research, but I believe it must be a 'red' dash light before it is in violation. A yellow warning light is merely a 'get repaired soon' type of thing.
I did want to throw in, regarding the AMU issues discussed in the past on M2's, I wanted to update I replaced AMU #3 again, but this time it lasted 590,000 mi.s after installing it with the clamping method. When I pulled it, it was again apparent dirt, and more likely salt, had worked it's way past the rubber gaskets with the molded in o-rings. Before I started squeezing the AMU's together when mounting, I was replacing the #3 every 80,000 mi.s or so.
Hope this helps.
