On numerous occasions, when I've pressed the brake pedal firmly (not slamming on it), my brakes have locked up and my tires skid. From what I can tell, just one of the tires is leaving a skid mark (rear passenger, I believe). I would expect the ABS to work the same way it has in every vehicle I've owned before this one but it hasn't in the 4 years I've owned it. This has happened to me at least a half dozen times slowing down from 40-45 miles per hour. The first time it happened I didn't think too much of it but now I'm thinking there's an issue. My dash isn't lit up with warning lights so I would think that my ABS should be working. Has anybody experienced this problem? Possibly an ABS sensor issue?