Dodge RAM TRUCK 1500 1995 Service Manual page 209

BR
ALL-WHEEL ANTILOCK BRAKE SYSTEM (ABS) 5 - 37
braking. The solenoid valves are activated only when
braking effort and rate of wheel slip and deceleration
exceed normal limits.
MASTER
CYLINDER
ASSEMBLY
RWAL
VALVE J9405-76
Fig. 2 RWAL Waive And Combination Waive Location
Combination Valve
The combination valve used with the ABS system
contains a front disc brake metering valve and a
front/rear pressure differential valve and switch.
The metering valve controls fluid apply pressure to
the front disc brake calipers. Caliper apply pressure
is temporarily limited until the rear drum brake-
shoes contact the drum surface. This feature provides
balanced front/rear braking.
The pressure differential valve is connected to the
front and rear brake hydraulic systems. A leak in ei­
ther part of the system will actuate the valve causing
it to shuttle toward the leaking side of the system.
Movement of the valve trips the warning switch
plunger which closes the electrical circuit to the red
warning light.
The combination valve is permanently attached to
its mounting bracket. The valve bracket is also used
to mount the rear brake antilock valve (Fig. 3).
Combination valve operation and testing is fully
described in the antilock system diagnosis section.
Refer to this information when diagnosing system
faults.
ABS Control Module
A separate electronic control module is used to
monitor and operate the ABS system. The module is
located at the drivers inner fender panel (Fig. 1). The
module is attached to the forward side of the front
antilock valve mounting bracket.
COMBINATION
VALVE
AND MOUNTING
BRACKET
ASSEMBLY
J9405-96
Fig. 3 Combination Waive And integral Mounting
Bracket
The module controls front/rear valve solenoid oper­
ation during all phases of antilock braking. Module
electrical inputs are provided by wheel speed signals
from the front and rear wheel speed sensors.
ABS Diagnostic Connector
The ABS diagnostic connector is at the underside of
the knee bolster. The connector is a six-way style and
is either black, or blue in color. The connector is the
ABS access point for the DRB scan tool. System cir­
cuits can be checked once the scan tool is plugged
into the connector.
Wheel Speed Sensors And Tone Wheels
Three wheel speed sensors are used in the ABS
system. A separate sensor is used at each front
wheel. A single sensor is used for both rear wheels
(Fig. 4).
The sensors convert wheel speed into an electrical
signal. The signal is transmitted to the electronic
control module for processing.
The trigger mechanism for each front wheel sensor
is a gear-type tone wheel. The tone wheels are
mounted on the inboard side of the disc brake rotor
hub (Fig.
5).
A single sensor is used to monitor rear wheel speed
and rate of deceleration. The sensor is mounted at
the top of the rear axle housing (Fig. 6). The trigger
mechanism for the sensor, is an exciter ring pressed
onto the differential case next to the ring gear.
The teeth on the tone wheels and exciter ring in­
terrupt the sensor magnetic field as they rotate. The
rate of interruption is converted into speed signals
which are transmitted to the electronic control mod­
ule.
The front and rear sensors are fixed and not ad­
justable. A front or rear sensor must be replaced
when diagnosis indicates a fault has occurred.
Master Cylinder And Power Brake Booster
A standard master cylinder and vacuum power
brake booster are used with the ABS system. The