I'd agree check ABS sensors, but the Focus doesn't use toothed wheels.

It uses segmented magnetic rings as the rotating element. At the front they are integral in the bearing so well shrouded by the Knuckle and CV. At the rear they are a push on fit on the back of the hub.

Any problems I've had have been fixed with a bit of WD40 (or real contact cleaner) in the weatherproof 2 pin connector.

Martin