Three-Channel 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.
• 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 in the engine compartment on the LH shock tower.
• Rear axle speed sensor - the sensor is located in the rear differential housing and can be serviced separately.
• Rear axle speed sensor tone ring - the tone ring is located on the rear differential case. It can be serviced separately from the differential, but the ring gear must be removed in order to do so.
• Brake pressure transducer (if equipped), which is mounted on the underside of the master cylinder toward the rear of the vehicle.

ABS aids in the prevention of wheel lock-up during braking events, which allows 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)