How does a speed sensor work?

Answer 1

Think of a speed sensor as a small generator. The faster you go the more current it produces. Each wheel speed sensor sends that current to a module and the module monitors them. With the vehicle in motion all the wheel speed sensors should read about the same amount of current. When you hit the brakes hard and one wheel locks up because of ice or whatever the module stops receiving current from that one wheel because it is no longer turning. The module now sends a signal to the abs valve block to relieve the brake pressure to that wheel to allow it to spin again. That wheel begins to spin again and it sends current back to the module. This process happens several times a second until all the wheel speed sensors read the same again.