Anti-Lock Brake System (ABS)
GENERAL DESCRIPTIONFEATURES
The 4ABS ensures directional stability and control during hard braking.
This ABS uses a 4-sensor 4-channel system that controls all four wheels independently of each other.
^ EBD (Electronic Brake-force Distribution system) control has been installed to provide the ideal braking force for the rear wheels.
EBD CONTROL
In ABS, electronic control is used so the rear wheel brake hydraulic pressure during braking is regulated by rear wheel control solenoid valves in accordance with the vehicle's rate of deceleration. The front and rear wheel slippages are calculated from the signals received from the various wheel sensors. EBD control is a control system which provides a high level of control for both vehicle braking force and vehicle stability. The system has the following features:
^ To shorten the harness wires and enhance data transmission reliability, communication with other ECU is performed over a CAN (Controller Area Network).
^ Fail-safe function ensures that safety is maintained.
^ Diagnostic function provides improved serviceability.
^ Because the system provides the optimum rear wheel braking force regardless of vehicle load and the condition of the road surface, the system reduces the required pedal depression force, particularly when the vehicle is heavily loaded.
^ Because the duty placed on the front brakes is reduced, the increases in pad temperature can be controlled during front brake application to improve pad wear.
^ Control valves such as the proportioning valve are not required.
CONSTRUCTION DIAGRAM
NOTE: On vehicles with ASC, the ABS system is controlled by the TCL/ASC-ECU.
SYSTEM CHECK SOUND
When starting the engine, a thudding sound can sometimes be heard coming from the engine compartment. This is a normal sound during the ABS self-check.
ABS OPERATION SOUNDS AND SENSATIONS
During normal operation, the ABS makes several sounds that may seem unusual at first:
^ A whining sound is caused by the ABS hydraulic unit motor.
^ When pressure is applied to the brake pedal, the pulsation of the pedal causes a scraping sound.
^ When the brakes are applied firmly, the ABS operates, rapidly applying and releasing the brakes many times per second. This repeated application and release of braking forces can cause the suspension to make a thumping sound and the tires to squeak.
LONG STOPPING DISTANCES ON LOOSE ROAD SURFACES
When braking on loose surfaces like snow-covered or gravel roads, the stopping distance can be longer for an ABS-equipped vehicle than the stopping distance for a vehicle with a conventional brake system.
SHOCK AT STARTING CHECK
Shock may be felt when the brake pedal is lightly pressed while driving at a low speed. This is a normal characteristic because the ABS system operation check is carried out when vehicle speed is 8 km/h (5 mph) or less.