[Canucklehead]

This is right out of AllData's Anti-Lock Brake Section for

Rear Wheel Anti-Lock System Description and Operation


SYSTEM DESCRIPTION
The system monitors rear axle rotation during braking. If axle speed decreases at a rate that indicates rear wheel lock-up, the system adjusts hydraulic pressure to the rear brakes.

System Design
The system is designed to minimize rear wheel lock-up under severe braking conditions or when traction is reduced due to slippery roads. Under normal operation, the vehicle braking system will function like a conventional braking system.

Lock-Up Condition
The Rear Wheel Antilock (RWAL) system works only when the brake pedal is applied and possible lock-up conditions exist. It cannot cause the brakes to be applied without the pedal being pressed.

Pedal Pulsation
Normally, the driver cannot tell when the RWAL system is operating. Occasionally, there may be a slight brake pedal pulsation when the RWAL system makes a pressure correction.

RWAL System Self-Check
The RWAL system conducts a system self-check when the ignition switch is turned on. The "Rr ABS" lamp will stay on for about two seconds after the engine starts, then goes out when the system finds no faults.

RWAL Maintenance
There is no scheduled routine maintenance for the RWAL system beyond the required normal brake system maintenance items. If any problem occurs in the normal brake system that causes the "BRAKE" indicator lamp to light, the RWAL system will disable itself and the "Rr ABS" indicator lamp will also come on.

RWAL Operation In 4WD
The RWAL system will operate while the vehicle is in 4-wheel drive (transfer case in 4L or 4H); however, if the front brakes lock in 4WD, the rear wheels will also lock, regardless of RWAL system operation, because they are mechanically connected to the front wheels through the transfer case.