Anti-Lock Brake System: Operation

Under normal conditions, Bendix-4 ABS functions the same as a standard brake system with a diagonally split master cylinder and conventional vacuum assist. If wheel lock is detected during brake application, system will enter anti-lock mode.

During anti-lock braking, hydraulic pressure in 4 wheel circuits is modulated to prevent any wheel from locking. Each wheel is designed with a set of valves and hydraulic lines to provide modulation. For vehicle stability, both rear wheel valves receive the same electrical signal. System can build or reduce pressure at each wheel, depending on signals generated by wheel speed sensors and sent to Controller Anti-Lock Brake (CAB).

During anti-lock braking, pressures are modulated by cycling electric solenoid valves. Cycling of these valves can be heard as a series of popping or ticking noises. In addition, cycling may be felt as a pulsation in brake pedal. If anti-lock operation occurs during hard braking, some pulsation may be felt in vehicle body due to fore and aft movement of suspension as brake pressures are modulated.

ABS is available and will operate at most vehicle speeds. ABS is automatically turned off at speeds less than 3 MPH. Wheel lock-up may be perceived at very end of anti-lock stop and is considered normal.

Red BRAKE light comes on, as a bulb check, when ignition switch is in START position. Light should go off when ignition is released. If light does not go off, it indicates one of the following possible problems: parking brake is not fully released, low brake fluid, low accumulator pressure or low hydraulic pressure.

NOTE: If only Amber ANTI-LOCK light is on (Red BRAKE light off), it indicates that only anti-lock functions have been disabled. Power-assisted normal braking is unaffected.

Amber ANTI-LOCK light comes on when CAB detects a condition which causes shutdown of anti-lock function. Amber ANTI-LOCK light is normally on until the CAB completes its self-tests and turns light off.