Our 01 Ambassador w/similar chassis did that on a regular basis. If the wheel bearings have worn a little allowing some slack, on a rough road, the wheel would wobble very slightly and push the sensor away. The remedy was to park and shut it off, go underneath and pull the sensor out a little and firmly push it back in. Start and drive for .5 miles plus and the light should go out if that was the difficulty. Once I had the wheel bearings re-torqued to 80+ ftlbs, did not have that trouble any more. This is only one of many possibilities however. Hope this may help, happy trails Bert