Anti-Lock Braking: Notes

The ABS consists of the following components:

• ABS module - attached to the Hydraulic Control Unit (HCU) and cannot be serviced separately from the HCU.
• HCU - which contains several valves (inlet, outlet, isolation and dump) and the hydraulic pump motor. The HCU is mounted on the RH side of the engine compartment and is serviced with the ABS module.
• Front wheel speed sensors - one sensor is located in each front wheel knuckle. The sensors are serviced separately from the knuckle.
• Rear wheel speed sensors - one sensor is located at each rear wheel end, is mounted to the brake backing plate and can be serviced separately.
• Wheel bearing magnetic strip - the wheel bearing magnetic strip is part of the wheel bearing and is serviced with the bearing.

ABS aids in the prevention of wheel lock-up during braking events allowing the driver to maintain steering control and stop in the shortest distance possible under most conditions. This is accomplished by the ABS module and HCU modulating brake fluid pressure to the affected brake caliper(s) and wheel cylinder(s).

When the ABS activates, the driver may notice the following operational symptoms:

• A rumble or grinding sound may be heard (HCU pump motor)
• If the driver's foot is on the brake pedal, a vibration may be felt in the brake pedal (HCU pump motor and valves)