Dodge RAM TRUCK 1500 1995 Service Manual page 199

B R
REAR WHEEL ANTILOCK liAKE (RWAL) SYSTEM 5 - 27
Electronic
Control
Module
The electronic module controls operation of the so­
lenoids in the rear brake antilock valve. The module
is separate from other electrical circuits in the vehi­
cle and operates independently.
The module is located under the central portion of
the instrument panel (Fig. 3). The module is accessi­
ble through the opening created by removal of the
knee bolster.
The RWAL valve, speed sensor and indicator lamps
are all in circuit with the module. The module con­
tains a microprocessor that operates the system and
performs system diagnostic checks.
Speed sensor inputs are continuously monitored
and interpreted by the module. The module deter­
mines wheel speed and rate of deceleration from
these inputs and activates the appropriate solenoid
in the hydraulic valve when necessary.
The module microprocessor also contains a self test
program. The program is activated when the ignition
switch is turned to the On position. In this mode, the
module checks indicator light operation, the system
electrical circuits and the pressure limiting valve so­
lenoids.
The brake warning and antilock indicator lamps
are illuminated for approximately two seconds during
the system self test cycle.
Fig. 3 RWAL Electronic Module And Bracket
Location
RWAL VALVE
The RWAL (rear brake antilock) valve controls rear
brake fluid apply pressure during antilock mode
braking. The valve is operated by the electronic con­
trol module. The valve is mounted on the combina­
tion valve bracket (Fig. 3).
The valve contains two solenoid valves that are in­
active during periods of normal braking. The solenoid
valves are activated only when braking effort and
rate of wheel slip and deceleration are high (antilock
mode).
During normal braking, the valves allows free flow
of brake fluid to the rear brake units. In antilock
mode, the valve will decrease, hold or increase fluid
apply pressure as needed.
Fig. 4 Combination Valve And RWAL Valve
Combination Valve
A combination valve is used with the RWAL sys­
tem. The valve is attached to an integral bracket
that is mounted to the studs on the power brake
booster. The valve bracket is also used to mount the
RWAL valve (Fig. 4). The mounting bracket and com­
bination valve are serviced as an assembly.
The combination valve contains a front brake me­
tering valve and a pressure differential switch and
valve. The differential switch is in circuit with the
red brake warning light.
The metering valve balances brake action between
the front disc and rear drum brakes. The valve
meters (holds-off) full apply pressure to the front disc
brakes until the rear brakeshoes are in full contact
with the drums.
SPEED SENSOR AND EXCITER RING
A speed sensor is used to transmit speed and rate
of deceleration inputs to the electronic control mod­
ule (Fig. 5). The sensor is actuated by an exciter ring
on the differential case.
The sensor is mounted at the top of the rear axle
housing directly over the gear-type exciter ring (Fig.
5). The exciter ring is pressed onto the differential
case adjacent to the ring gear.
The exciter ring is the sensor trigger mechanism.
Exciter ring rotation causes the teeth on the ring to
interrupt the magnetic field around the sensor pole.
The rate of interruption is converted into speed sig­
nals which are transmitted to the control module.
The sensor is not adjustable and must be replaced
whenever diagnosis indicates a fault has occurred.
The exciter ring is serviceable and can be replaced
when necessary.