i suppose the sensor on your hub could be going, but i would expect that once it goes, it goes. not sometimes be fine, other times not. i'm dealing with a similar issue with my regal right now, but i think i have the problem figured out. the issue that is plaguing my car is that there seems to be a questionable spot in the wire harness that goes from the hub up to the plug on the frame/body. most times it's fine, but typically if it does set off the lights, it's usually at highway speeds, but not always. my mechanic and i tested the harness similarly to how abrasive suggested earlier, but with the following modifications: raised car, unplugged wire harness at frame/body side, leaving the hub plugged in at the other end. used the multimeter to check resistance, then starting from the hub plug end slowly bending the wire harness back and forth, watching for infinite resistance (broken/poor wire) wires on the hub itself were fine, but once i got half way up the harness to the frame/body, bending the wire revealed that there was a bad spot, causing infinite resistance, or as the abs system saw it, an open/short. I had a spare harness i got from ed morad awhile back, but i didnt have it with me, it was in my garage so i have to jack the car up at home to change it instead of on a nice lift.