Anti-Lock Braking System (ABS)

What is an Anti-Lock Braking System (ABS)?

An ABS, a safety feature in most vehicles, helps the driver steer in the event of a sudden stop or need to brake during an emergency (inclement weather, etc.). The system helps prevent your tires from locking up.

It is important to note, that on most surfaces, a vehicle equipped with ABS will stop faster than a vehicle without it. On soft surfaces (e.g., gravel, snow), ABS may increase stopping distance while allowing drivers to keep steering control. This is an ideal scenario for drivers as the lack of wheel rotation causes that would be needed to stop.

How Does an ABS Work?

In a heavy stopping event, once the driver applies the brakes, the ABS will cycle the brake pressure when the wheels lockup.

Here are the four components that make up the ABS:

  • Speed sensors monitor the speed of each wheel and determine the acceleration or deacceleration of each wheel
  • Valves are located within the brake line and control the pressure to the brake
  • Pumps apply pressure to the brake drums/calipers when the brakes are applied
  • Electric Control Unit (ECU) processes the speed sensor information, and it rapidly cycles the brake pressure on and off through valves and pumps

To mitigate the occurrence of malfunctions, brake systems must be routinely serviced in accordance with the vehicle Owner’s Manual to perform properly.

Types of ABS

U.S. federal law requires all cars and minivans made in or after 2012 must have four-wheel ABS. Here are diverse types of ABS:

  • Four channel, four sensor ABS has speed sensors and valves on all four wheels. This system offers the best traction control as each individual wheel is monitored for potential lock-up
  • Three channel, four sensor ABS has speed sensors for all four wheels, separate valves for front wheels and single valve for the rear wheels
  • Three channel, three sensor ABS has speed sensors and valves on both front wheels and the rear wheels share a speed sensor and valve; both rear wheels must lock up to trigger ABS

A driver will know if their car is equipped with ABS by either - (1) reading the vehicle’s Owner’s Manual, (2) checking the instrument panel for an ABS indicator light after turning on the ignition, or (3) asking the dealer or rental car company.

Benefits of ABS

  • Manages wheel lockup or reduces wheel lockup
  • Helps reduce stopping distances during emergency braking situations, such as wet and slippery road surfaces – but can vary depending on the surface (e.g., gravel or unpacked snow)
  • Maintain directional stability and control over steering (four-wheel ABS only)

Anti-Lock Brakes vs Conventional Brakes

Conventional brakes are operated by the driver under normal operating conditions. The ABS system is operated by the electronic control unit (ECU) and triggered through the wheel speed sensors during an emergency braking event. Both systems apply and release pressure through the same hydraulic brake fluid system or air brake system depending on design.

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