Dodge ram truck 3500 1996 Service Manual page 232

I - 4S BRAKES
B R
DESCRIPTION AND OPERATION ( C o n t i n u e d )
RWAL SYSTEM COMPONENTS
CONTROLLER ANTILOCK BRAKES
The Controller Antilock Brakes (CAB) is a micro­
processor which monitors and controls the ABS brake
system operation (Fig. 2). I t has a 14 terminal con­
nector to deliver power and ground to the CAB and
connect all inputs and outputs associated with the
ABS system. The CAB primary functions are:
® Detect wheel locking tendencies.
• Control the application of brake fluid pressure to
the rear brakes during antilock braking.
• Monitor the RWAL brake system for proper oper­
ation.
• Perform self-check diagnostics.
RWAL
C O N T R O L L E R ANTILOCK
B R A K E S
8031e890
Fig. 2 RWAL CAB
The CAB continuously monitors the speed of the
differential ring gear by monitoring signals generated
by the rear wheel speed sensor. The CAB determines
a wheel locking tendency when i t recognizes the ring
gear decelerating too rapidly.
When a wheel-locking tendency is detected, - the
CAB energizes the isolation solenoid in the RWAL
valve. When the isolation solenoid is energized,
hydraulic pressure cannot be increased to the rear
wheel cylinders. I f the rear wheel speed sensor still
indicate that the ring gear is decelerating too rapidly,
the CAB then energizes the dump solenoid to reduce
pressure at the rear wheel cylinders. The CAB con­
tinues this action until the wheel-locking tendency no
longer exists.
When a fault is detected, the CAB will generate
and store diagnostic trouble codes. Only one code can
be stored at any one time. I f the CAB senses a fault
in any one of its monitored circuits, i t will illuminate
the red brake warning and ABS warning lamps. I t
will then generate a Diagnostic Trouble Code (DTC)
and store i t i n memory. I n general, the diagnostic
trouble code will remain i n memory when the igni­
tion key has been turned OFF. The exception to this
is codes 9 and 11 which are erased any time the key
has been turned OFF. Also, code 11 will be removed
from memory when the ignition is in the RUN or
ACC. positions i f the malfunction that caused the
code has been eliminated. For both codes 9 and 11, i f
the malfunction remains, the DTC will be reset on
the next ignition key cycle to ON.
Cab Inputs
The CAB monitors the following inputs to deter­
mine when a wheel locking tendency may exists:
• Rear Wheel Speed Sensor
© Brake Lamp Switch
® Brake Warning Lamp Switch
• Reset Switch
• 4WD Switch (If equipped)
Cab Outputs
The CAB controls the following outputs for antilock
braking and brake warning information:
• RWAL Valve
® ABS Warning Lamp
• Brake Warning Lamp
Power Supply And Ground
Ignition voltage is provided to the CAB through
pin 3 and is protected by a 20 amp fuse. Ignition
voltage is supplied when the ignition switch is in the
RUN or ACC. positions. The CAB requires ignition
voltage to be able to operate the function of antilock
brakes. Battery voltage is provided to the CAB
through pin 9 and is protected by a 20 amp fuse.
This circuit supplies power to the memory cells so
that the CAB can retain diagnostic information.
Except for trouble codes 9 and 11, the CAB stores
DTCs in the battery fed volatile memory. Volatile
memories only retain information as long as power is
supplied to the memory. I f a DTC is stored in the
battery fed volatile memory, the DTC can be cleared
from the memory by disconnecting the battery supply
to the CAB. Trouble codes 9 and 11 are also in a vol­
atile memory but their memories are fed with igni­
tion voltage. A ground is provide to the CAB through
pin 12 of the 14-way connector. I t is required by the
CAB to be able to operate any of its circuits.
REAR WHEEL SPEED SENSOR AND EXCITER
RING
The rear Wheel Speed Sensor (WSS) is mounted in
the rear differential housing (Fig. 3). The WSS con­
sists of a magnet surrounded by windings from a sin-