On the vehicles in question, two types of systems are used: rear brake release system (RWAL system) and front and rear brake release system (4WAL system). The RWAL system only controls the brakes on the rear wheels, while the 4WAL system distributes braking to all wheels.
Actuator
It consists of a master cylinder and a control valve, which includes a bypass valve and a shut-off valve. The valve provides a change in fluid pressure in the hydraulic circuit in accordance with the signals from the control unit.
Control block
ABS control unit - the system has a name «Electro-hydraulic control unit» (EHCU) on vehicles with 4WAL system and «Control block» on vehicles with RWAL system. The control unit is installed in the engine compartment, under the main cylinder (see photo). The block receives signals from the brake signal switch and speed sensors of each wheel, on the basis of which the pressure in the hydraulic drive of this wheel is regulated. If the wheel rotation speed differs from the base one, the control unit opens the actuator valve and the fluid under excess pressure flows into the tank. The wheel is partially released. After equalizing the speed of rotation, the valve closes and the pressure builds up again. Numerous repetition of such cycles stabilizes the speed of rotation of all wheels and increases the stability of the car. The control unit also has a self-diagnosis function.
When the system fails, the BRAKE sign lights up on the dashboard (on vehicles with RWAL system) or ANTI-LOCK (on vehicles with 4WAL system).
Speed sensor
On vehicles with the 4WAL system, speed sensors are installed on each wheel. On vehicles with the RWAL system, the wheel speed sensor is mounted in the shank of the transmission housing on rear-wheel drive models, and in the transfer case on all-wheel drive models. The speed sensor generates a signal that goes to the control unit, indicating the speed of rotation of the wheel.
Stop signal switch
The brake light switch informs the control unit when the brake pedal is depressed. In the absence of this signal, the anti-lock braking system will not work.
Diagnostics and repair
The system is serviced in a car service. However, you can perform the following checks yourself.
- A) Make sure the calipers and brake cylinders are in good condition.
- b) Check the wire connectors in the control box.
- V) Check fuses.
- G) Check the integrity of the wiring of the speed sensors and the brake light switch.