Description & Operation
The Anti-lock Brake System (ABS) controls fluid pressure applied to front and rear brakes to prevent any wheel from locking during hard braking. Wheel speed sensors, located at each wheel, detect wheel rotation speed and send a signal to ABS hydraulic unit/control module assembly (located at left rear side of engine compartment, near shock tower). See Fig 1 . The ABS hydraulic unit/control module assembly combines ABS hydraulic unit, ABS control module, actuator assembly, pump motor relay and fail-safe relay into one unit. The ABS hydraulic unit controls fluid pressure in response to signals from ABS control module. A hydraulic pump boosts fluid pressure in case of low fluid pressure. Fail-safe relay supplies power to solenoid valve in ABS hydraulic unit and pump motor relay. Pump motor relay supplies power to pump motor in ABS hydraulic unit.
When wheel speed sensor signals indicate an impending wheel lock-up condition, ABS control module calculates vehicle deceleration speed and sends a signal to hydraulic unit to modulate brake fluid pressure, thus preventing wheel lock-up. ABS hydraulic unit/control module assembly has a self-diagnostic capability. If an abnormality is detected in system, ABS hydraulic unit/control module assembly activates the ABS warning light relay located in engine compartment fuse/relay block and relay turns ABS warning light on.