Anti-Lock Brake System
The Anti-Lock Brake System (ABS) keeps wheels from locking up under extreme braking conditions. ABS prevents excessive wheel slip by pulsing modulation of brake pressure. Hydraulic and Electronic Control Unit (HECU) monitors wheel speed. If any wheel slows too quickly (approaches lock-up) during brake actuation, HECU will signal modulator assembly to reduce hydraulic pressure to that wheel to prevent lock-up.
ABS system consists of wheel speed sensors, rotors with exciter rings (tone rings), ABS warning light and HECU. See Fig 1 . HECU contains control module electronics, ABS solenoids and ABS pump motor.