<P> In 1993, Lincoln became one of the first automobile companies to provide standard four - wheel anti-lock brakes on all of their vehicles . </P> <P> The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake). </P> <P> Typically ABS includes a central electronic control unit (ECU), four wheel speed sensors, and at least two hydraulic valves within the brake hydraulics . The ECU constantly monitors the rotational speed of each wheel; if it detects a wheel rotating significantly slower than the others, a condition indicative of impending wheel lock, it actuates the valves to reduce hydraulic pressure to the brake at the affected wheel, thus reducing the braking force on that wheel; the wheel then turns faster . Conversely, if the ECU detects a wheel turning significantly faster than the others, brake hydraulic pressure to the wheel is increased so the braking force is reapplied, slowing down the wheel . This process is repeated continuously and can be detected by the driver via brake pedal pulsation . Some anti-lock systems can apply or release braking pressure 15 times per second . Because of this, the wheels of cars equipped with ABS are practically impossible to lock even during panic braking in extreme conditions . </P> <P> The ECU is programmed to disregard differences in wheel rotative speed below a critical threshold, because when the car is turning, the two wheels towards the center of the curve turn slower than the outer two . For this same reason, a differential is used in virtually all roadgoing vehicles . </P>

When does anti lock brakes start to work
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