Antilock Brakes / Traction Control Systems: Description and Operation

Purpose
The Anti-Lock Brake System (ABS) consists of electronic and hydraulic components. It allows for control of braking force so locking of the wheels can be avoided.
1. Improves proper tracking performance through steering wheel operation.
2. Eases obstacle avoidance through steering wheel operation.
3. Improves vehicle stability.

Operation
- When the vehicle speed is less than 10 km/h (6 MPH), this system does not work.
- The Anti-Lock Brake System (ABS) has a self-test function. The system turns on the ABS warning lamp for 1 second each time the ignition switch is turned "ON". After the engine is started, the ABS warning lamp turns off. The system performs a test the first time the vehicle reaches 6 km/h (4 MPH). A mechanical noise may be heard as the ABS performs this self-test. This is a normal part of the self-test feature. If a malfunction is found during this check, the ABS warning lamp will stay on.
- While driving, a mechanical noise may be heard during ABS operation. This is a normal condition.





ABS Hydraulic Circuit





System Components

System Description
SENSOR





The sensor unit consists of a gear-shaped sensor rotor and a sensor element. The element contains a bar magnet around which a coil is wound. The front sensors are installed on the front spindles and the rear sensors are installed on the rear spindles. As the wheel rotates, the sensor generates a sine-wave pattern. The frequency and voltage increase(s) as the rotating speed increases.

CONTROL UNIT (BUILT-IN ABS ACTUATOR AND ELECTRIC UNIT)





The control unit computes the wheel rotating speed by the signal current sent from the sensor. Then it supplies a DC current to the actuator solenoid valve. It also controls ON-OFF operation of the valve relay and motor relay. If any electrical malfunction should be detected in the system, the control unit causes the warning lamp to light up. In this condition, the ABS will be deactivated by the control unit, and the vehicle's brake system reverts to normal operation.

ABS ACTUATOR AND ELECTRIC UNIT





The ABS actuator and electric unit contains:
- An electric motor and pump
- Two relays
- Eight solenoid valves, each inlet and outlet for
- LH front
- RH front
- LH rear
- RH rear

- ABS control unit
This component controls the hydraulic circuit and increases, holds or decreases hydraulic pressure to all or individual wheels. The ABS actuator and electric unit is serviced as an assembly.





ABS Actuator Operation