Antilock Brakes / Traction Control Systems: Description and Operation

The anti-lock brake system adjusts the brake pressure whenever a wheel is about to lockup, allowing the driver to maintain greater control of the vehicle under heavy braking conditions. Under normal driving conditions, the anti-lock brake system (ABS) works the same way as a standard power assisted brake system.

The Electronic Brake Control Module (EBCM) receives inputs from individual ABS speed sensors and the G-sensor. The electronic brake control module (EBCM) uses the inputs to control the ABS hydraulic unit, which adjusts the hydraulic pressure applied to each caliper on the basis of the signals received from the electronic brake control module (EBCM).

The electronic brake control module (EBCM) has a self-diagnosis function which turns on the "ABS" indicator light and disables the anti-lock braking function when it detects a problem. The standard power assisted brake system will continue to operate normally.


Rear Wheel ABS

The rear wheel anti-lock (RWAL) system continuously monitors rear wheel rotation during braking and corrects rear brake pressure to prevent full rear wheel lockup and provides more rear end stability. The system functions by regulating the rear hydraulic brake line pressure. The pressure regulation is accomplished by an anti-lock valve which is located on the right side frame rail. The anti-lock valve is made up of two valves, a dump valve which releases pressure into an accumulator and an isolation valve which maintains rear brake pressure. The valve is controlled by a microcomputer which is part of the Electronic Control Module (ECM).


Four Wheel ABS

The anti-lock brake system works on all four wheels. A combination of wheel speed sensor and electronic brake control module (EBCM) determines when a wheel is about to stop turning and adjusts brake pressure to maintain best braking. This system helps the driver maintain greater control of the vehicle under heavy braking conditions.