Editing Anti-lock braking system (section)

== Operation ==
The anti-lock brake controller is also known as the CAB (Controller Anti-lock Brake).<ref>{{cite web |author=((KI4CY)) |url=http://dodgeram.org/tech/specs/glossary.htm |title=Ram Glossary of abbreviations and terms |website=Dodgeram.org |date=2003-02-13 |access-date=2010-12-07 |archive-url=https://web.archive.org/web/20101122091356/http://dodgeram.org/tech/specs/glossary.htm |archive-date=22 November 2010 }}</ref>

Typically ABS includes a central [[electronic control unit]] (ECU), four [[wheel speed sensor]]s, and at least two hydraulic valves within the brake [[Hydraulic brake|hydraulics]]. The ECU constantly monitors the [[rotational speed]] of each wheel; if it detects the wheel rotating significantly slower than the speed of the vehicle, 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.<ref name="Erjavec2000">{{cite book |url=https://books.google.com/books?id=3AJxi5DzoBcC&q=can+modulate+the+pressure+to+the+brakes+as+often+as+15+times+per+second.&pg=PA1197 |title=Automotive Technology: A Systems Approach |author=Jack Erjavec |publisher=Cengage Learning |year=2000 |isbn=0-7668-0673-1 |pages=1197–}}</ref><ref name="HowStuffWorks ABS 2010">Nice, Karim. [http://auto.howstuffworks.com/auto-parts/brakes/brake-types/anti-lock-brake1.htm How "Anti-Lock Brakes Work"]. [http://www.howstuffworks.com/about-hsw.htm howstuffworks]. Retrieved October 2, 2010.</ref> Because of this, the wheels of cars equipped with ABS are practically impossible to lock even during panic braking in extreme conditions.

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 (mechanics)|differential]] is used in virtually all roadgoing vehicles.

If a fault develops in any part of the ABS, a warning light will usually be illuminated on the vehicle instrument panel, and the ABS will be disabled until the fault is rectified.

Modern ABS applies individual brake pressure to all four wheels through a control system of hub-mounted sensors and a dedicated [[micro-controller]]. ABS is offered or comes standard on most road vehicles and is the foundation for electronic stability control systems, which are rapidly increasing in popularity due to the great reduction in the price of vehicle electronics over the years.<ref name="absfaq">{{cite web |url=http://www.abs-education.org/faqs/faqindex.htm |title=ABS Frequently Asked Questions |publisher=ABS Education Alliance |date=2004-05-03 |access-date=2009-10-22 |archive-url=https://web.archive.org/web/20100523233624/http://www.abs-education.org/faqs/faqindex.htm |archive-date=23 May 2010}}</ref>

Modern electronic stability control (ESC) systems are an evolution of the ABS concept. Here, a minimum of two additional sensors are added to help the system work: these are a [[steering wheel]] angle sensor and a [[Gyroscope|gyroscopic]] sensor. The theory of operation is simple: when the gyroscopic sensor detects that the direction taken by the car does not coincide with what the steering wheel sensor reports, the ESC software will brake the necessary individual wheel(s) (up to three with the most sophisticated systems), so that the vehicle goes the way the driver intends. The steering wheel sensor also helps in the operation of [[Cornering Brake Control]] (CBC), since this will tell the ABS that wheels on the inside of the curve should brake more than wheels on the outside, and by how much.

ABS equipment may also be used to implement a [[traction control system]] (TCS) on the acceleration of the vehicle. If, when accelerating, the tire loses traction, the ABS controller can detect the situation and take suitable action so that traction is regained. More sophisticated versions of this can also control throttle levels and brakes simultaneously.

The speed sensors of ABS are sometimes used in indirect [[tire pressure monitoring system]] (TPMS), which can detect under-inflation of the tire(s) by the difference in the rotational speed of wheels.