I haven't seen the problem/query prior to your comment but... when your ABS is operating you will hear an alarming juddering noise and feel it through the brake pedal - that is normal and good assuming your ABS should be operating ie on a slippy surface. In normal driving on a good surface your ABS should not operate at all although the four wheel sensors are constantly monitoring things in case ABS is needed. When my ABS has misbehaved the ABS light illuminates and it ceases to function. Once it was a faulty sensor (9yrs old and £30 to replace DIY) and on two other occasions it was the segmented ring on one of the front wheels which had cracked and was therefore no longer turning with the wheel, confusing the ABS electronics. I was able to repair that at no cost but time. It could be a number of things but most likely a sensor on its way out - but which one?!
Hope some of that helps - a little!
Richard, January 2009
