Figure 15.70. Elements of the anti-lock braking system: 1 – hydraulic device; 2 – front wheel speed sensor rotor; 3 – front wheel speed sensor; 4 – diagnostic connector; 5 – rear wheel speed sensor; 6 – rear wheel speed sensor rotor; 7 – control unit; 8 – relay block
Some 1987-model vehicles are equipped with rear disc brakes, while some 1988-model vehicles are additionally equipped with an anti-lock braking system (ABS). The ABS, installed since 1988, is designed to improve vehicle stability under heavy braking. This is achieved by monitoring the rotation speed of each wheel and controlling the pressure in the brake system, which prevents the wheels from locking. A yellow warning lamp in the instrument cluster indicates a system malfunction. The anti-lock braking system consists of a hydraulic unit, a relay unit, a control unit and wheel speed sensors (figure 15.70). The control unit is located in the passenger compartment and is essentially the "brain" of the system, receiving and processing signals from the wheel speed sensors and generating commands to control the relay unit and the hydraulic device. Due to the complexity of the device, it is advisable to have the system diagnosed and repaired by a car service center. When working near the wheels, brake system or suspension of the vehicle, be careful not to damage the wheel speed sensors.