Anti-Lock Braking: Notes

The ABS consists of the following components:

• ABS module - attached to the Hydraulic Control Unit (HCU), but can be serviced separately from the HCU.
• Front wheel speed sensors - one sensor is located in each front wheel knuckle. The sensors are serviced separately from the knuckle.
• Front wheel speed sensor tone rings - the tone ring is a magnetic strip that is part of the front wheel bearing and is serviced with the bearing.
• HCU - which contains several valves (inlet, outlet, isolation and dump) and the hydraulic pump motor. The HCU is mounted on the LH side of the engine compartment underneath the brake master cylinder and brake booster.
• 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.
• Rear wheel speed sensor tone rings - one tone ring is located next to each rear wheel hub and is serviced separately.

ABS aids in the prevention of wheel lock-up during braking events which will allow 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)