Rear wheel antilock


Rear Wheel Antilock (RWAL) brake system is standard equipment. The RWAL brake system is designed to prevent rear wheel lock-up under heavy braking conditions on virtually all types of road surfaces.

RWAL braking is desirable because a vehicle which is stopped without locking the wheels will retain directional stability. This allows the driver to retain greater control of the vehicle during braking.

The RWAL components include:

  • Rwal valve
  • Controller Antilock brake (CAB)
  • Rear Wheel Speed Sensor (WSS)


When the brakes are applied, hydraulic fluid is routed from the master cylinder's secondary circuit, through the combination valve, to the RWAL valve.

From there hydraulic fluid is routed to the rear brake wheel cylinders. The Controller Antilock Brake monitors rear wheel speed through the rear wheel speed sensor. If a wheel is about to lock-up, the CAB signals the RWAL valve. The RWAL valve modulates the hydraulic brake pressure to the rear wheels to prevent wheel lock-up.


During light brake application, rear wheel deceleration is not sufficient to activate the antilock system components. During a normal stop hydraulic brake fluid flows unrestricted to the rear wheel cylinders to stop the vehicle. The antilock solenoid valves are inactive. The isolation valve is open and the dump valve is closed allowing normal fluid flow to the rear wheel cylinders.


If the CAB senses impending rear wheel lock-up, it will energize the isolation solenoid. This prevents a further increase of driver induced brake pressure to the rear wheels. If this initial action is not enough to prevent rear wheel lock-up, the CAB will momentarily energize a dump solenoid. This opens the dump valve to vent a small amount of isolated rear brake pressure to an accumulator. The action of fluid moving to the accumulator reduces the isolated brake pressure at the wheel cylinders. The dump (pressure venting) cycle is limited to very short time periods (milliseconds). The CAB will pulse the dump valve until rear wheel deceleration reaches the desired slip rate programmed into the CAB. The system will switch to normal braking once wheel locking tendencies are no longer present.

Rwal component location


RWAL CONTROLLER Driver side inner fender on a bracket. Tests, monitors and controls the rear brake system.
HYDRAULIC CONTROL UNIT/ RWAL VALVE Driver side inner fender on a bracket. Modulates hydraulic pressure to rear brakes during an RWAL stop.
REAR WHEEL SPEED SENSOR Top of the rear axle housing. Sends an AC voltage sinewave to the CAB whose frequency is proportional to vehicle speed
EXCITER RING Ring gear inside the differential housing. Used to pull the magnetic field across the wheel speed sensor's windings.
RED BRAKE WARNING LAMP Instrument cluster. Indicator for park brake engagement, hydraulic brake malfunction, or RWAL malfunction.
AMBER ABS WARNING LAMP Instrument cluster Indicator of an RWAL malfunction
BRAKE WARNING LAMP DIODE Instrument panel harness near the parking brake switch. Isolates the park brake switch circuit from the CAB for proper red brake warning lamp operation.
ISOLATION AND DUMP VALVE FUSE Inside the CAB. Fail-safe device for unwanted control of the isolation and dump solenoid/valves
ISOLATION AND DUMP SOLENOID/VALVES Inside the HCU/RWAL valve. Used to modulation hydraulic pressure to the rear brakes during an RWAL stop.

    Dodge Durango (DN) 1998-2003 Service Manual


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