depending on the set up it can have to senors one on each wheel. most likely there is dirt in the sensor or something sticking to the sensor or a broke or wet connector. if you have an ohm meter you can get for ten buck pull each wheel off one at a time unplug the ABS sensor going to the rotor and put the ohm meter on 12 volts DC spin the wheel in a forward direction if it produces 2 1/2 volts it's ok keep doing this to each wheel when you find one that does not give a voltage then that's where your problem lies and you will have to replace it or the magnet. If all of them ar ok then you need to raise the car up on jack stands and push on the brakes slowly and see if each wheel catches at the same spot, if you have on turning that could be your problem. If that does not Help then I can tell you it will go into default mode and will work like standard brakes, and if it's Beyond that then it need to go t a shop as they are expensive to work on if you don't know what your doing. and if this fixes it or helps you to locate it you just saved $150.00 to $200.00 bucks.
