The anti-lock brake system (ABS) sensors in most passenger vehicles are pressed into a hole in the steering knuckle and secured to the knuckle with a small metric bolt. As the vehicle ages, rust and grime accumulates around these sensors, making them difficult to remove. These sensors can easily be removed by dissolving the rust and road grime with aerosol penetrating oil and gently prying the sensor away from the knuckle.
Shift the vehicle's transmission into park (automatic) or first gear (manual). Turn off the engine, set the parking brake and open and secure the bonnet. Disconnect the negative battery cable from the battery with a battery terminal wrench.
Raise the front of the vehicle with a jack and support it with jack stands. Chock the rear wheels.
Slide underneath the vehicle and locate the ABS sensor you wish to remove. Remove the small metric bolt securing the ABS sensor to the steering knuckle with a 1/4-inch ratchet and a metric socket. Unplug the sensor's electrical connector. Spray the sensor and steering knuckle liberally with penetrating oil and allow it to sit for 10 minutes.
Insert a small flathead screwdriver between the ABS sensor and the steering knuckle. Gently pry the ABS sensor away from the steering knuckle until it is free.
Aerosol penetrating oil is available from auto parts and hardware stores.