Chrysler RAM TRUCK 2500 1994 Service Manual page 195

5 - 36 ALL-WHEEL ANTILOCK BRAKE SYSTEM (ABS)
of brake fluid to the rear brake units during normal
braking. The solenoid valves are activated only when
braking effort and rate of wheel slip and deceleration
exceed normal braking limits.
MASTER
CYLINDER
ASSEMBLY
RWAL
VALVE
J9405-76
Fig. 2 RWAL Valve And Combination Valve 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 i n 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 plunger type warn­
ing switch. The switch then closes the electrical cir­
cuit to the red warning light i n the instrument panel.
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 i n the antilock system diagnosis section.
Refer to this information when diagnosing system
faults.
ABS Electronic Control Module
A separate electronic control module is used to
monitor and operate the ABS system.
The ABS module is located at the drivers inner
fender panel under the battery and battery tray (Fig.
COMBINATION
VALVE
AND MOUNTING
BRACKET
ASSEMBLY
J9405-96
Fig. 3 Combination Valve And Integral Mounting
Bracket
1). The module is attached to the forward side of the
front antilock valve mounting bracket.
The module controls antilock valve solenoid opera­
tion during all phases of antilock braking. Module
electrical inputs are provided by wheel speed signals
from the front and rear sensors.
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 for identification purposes.
The connector is the ABS access point for the DRB I I
scan tool. The system components can be checked once
the scan tool is attached to the connector.
Wheel Speed Sensors And Tone Wheels
Three wheel speed sensors are used i n the all
wheel ABS system. A sensor is used at each front
wheel. A single sensor is used for both rear wheels
(Fig. 4).
ABS
FRONT
SENSOR
SENSOR
WIRE
STEERING
KNUCKLE
SENSOR
BOLTS
(21-25 N - m /
1 9 - 2 5 0 in. lbs
SPLASH
SHIELD
J9405-177
Fig. 4 Front Wheel Sensor Location