The Ford Focus has an anti-lock braking system (ABS) with sensors on each wheel that continuously monitor that wheel's speed. The ABS wheel sensor transmits this information to the ABS controller, which determines the amount of braking force to apply to that wheel during an emergency stop. The most common reason for replacing the ABS wheel sensor is metallic debris such as brake dust clogging the sensor.
Determine which ABS wheel sensor your Ford Focus will need. You'll want to be sure the new wheel sensor is compatible with your make and model of Focus. All versions of the Focus have ABS.
Disconnect the negative battery cable from the battery with a socket wrench and isolate it to prevent accidental contact with the battery.
Unplug the electrical connector for the wheel speed sensor and disconnect its mounting bolt with a socket wrench. Detach the wheel speed sensor from the vehicle.
Install the new wheel speed sensor and tighten the mounting bolt to 80 in. lbs. with a torque wrench. Plug in the electrical connector for the sensor to the body wiring harness.
Lower the vehicle and reattach the negative battery cable with a socket wrench.
Start the vehicle and clear any faults as needed until the ABS light does not come on. Drive the vehicle on a road that is fairly smooth and level so the tires can grip the road equally. Apply the brakes a few times to ensure proper ABS operation.