Dodge Durango (DN). Manual — part 248
EXCITER RING
The exciter ring is mounted on the differential
case. If the ring is damaged refer to Group 3 Differ-
ential and Driveline for service procedures.
SPECIFICATIONS
TORQUE CHART
DESCRIPTION
TORQUE
Controller
Mounting Screws . . . . . . . . . . 6 N·m (53 in. lbs.)
RWAL Valve
Mounting Bolt . . . . . . . 20-27 N·m (15-20 ft. lbs.)
Brake Line Fittings . . . . . . . 19 N·m (170 in. lbs.)
Wheel Speed Sensor
Mounting Bolt . . . . . . . . . . . 24 N·m (200 in. lbs.)
DN
BRAKES
5 - 39
REMOVAL AND INSTALLATION (Continued)
FOUR WHEEL ANTILOCK BRAKES
TABLE OF CONTENTS
page
page
DESCRIPTION AND OPERATION
ANTILOCK BRAKE SYSTEM . . . . . . . . . . . . . . . . 40
CONTROLLER ANTILOCK BRAKES . . . . . . . . . . . 41
HYDRAULIC CONTROL UNIT. . . . . . . . . . . . . . . . 41
WHEEL SPEED SENSOR. . . . . . . . . . . . . . . . . . . 42
ABS WARNING LAMP . . . . . . . . . . . . . . . . . . . . . 43
DIAGNOSIS AND TESTING
ANTILOCK BRAKES. . . . . . . . . . . . . . . . . . . . . . . 43
SERVICE PROCEDURES
BLEEDING ABS BRAKE SYSTEM . . . . . . . . . . . . 44
REMOVAL AND INSTALLATION
CONTROLLER ANTILOCK BRAKES . . . . . . . . . . . 44
ANTILOCK CONTROL ASSEMBLY . . . . . . . . . . . . 44
FRONT WHEEL SPEED SENSOR - 4x2 . . . . . . . . 45
FRONT WHEEL SPEED SENSOR - 4x4 . . . . . . . . 46
TONE WHEEL . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
REAR WHEEL SPEED SENSOR . . . . . . . . . . . . . 46
EXCITER RING . . . . . . . . . . . . . . . . . . . . . . . . . . 47
SPECIFICATIONS
TORQUE CHART . . . . . . . . . . . . . . . . . . . . . . . . . 47
DESCRIPTION AND OPERATION
ANTILOCK BRAKE SYSTEM
DESCRIPTION
The antilock brake system (ABS) is an electroni-
cally operated, all wheel brake control system.
The system is designed to prevent wheel lockup
and maintain steering control during periods of high
wheel slip when braking. Preventing lockup is accom-
plished by modulating fluid pressure to the wheel
brake units.
The hydraulic system is a three channel design.
The front wheel brakes are controlled individually
and the rear wheel brakes in tandem (Fig. 1). The
ABS electrical system is separate from other electri-
cal circuits in the vehicle. A specially programmed
controller antilock brake unit operates the system
components.
ABS system major components include:
• Controller Antilock Brakes (CAB)
• Hydraulic Control Unit (HCU)
• Wheel Speed Sensors (WSS)
• ABS Warning Light
OPERATION
Battery voltage is supplied to the CAB ignition ter-
minal when the ignition switch is turned to Run posi-
tion. The CAB performs a system initialization
procedure at this point. Initialization consists of a
static and dynamic self check of system electrical
components.
The static and dynamic checks occurs at ignition
start up. During the dynamic check, the CAB briefly
cycles the pump and solenoids to verify operation. An
audible noise may be heard during this self check.
This noise should be considered normal.
If an ABS component exhibits a fault during ini-
tialization, the CAB illuminates the amber warning
light and registers a fault code in the microprocessor
memory.
The CAB monitors wheel speed sensor inputs con-
tinuously while the vehicle is in motion. However,
the CAB will not activate any ABS components as
long as sensor inputs indicate normal braking.
Fig. 1 Antilock Brake System
1 – MASTER CYLINDER AND RESERVOIR
2 – POWER BRAKE BOOSTER
3 – WIRES TO WHEEL SPEED SENSORS
4 – RIGHT REAR WHEEL
5 – LEFT REAR WHEEL
6 – HYDRAULIC BRAKE LINES TO WHEELS
7 – COMBINATION VALVE
8 – HARNESS
9 – RIGHT FRONT WHEEL
10 – LEFT FRONT WHEEL
11 – CAB/HCU
5 - 40
BRAKES
DN
During normal braking, the master cylinder, power
booster and wheel brake units all function as they
would in a vehicle without ABS. The HCU compo-
nents are not activated.
The purpose of the antilock system is to prevent
wheel lockup during periods of high wheel slip. Pre-
venting lockup helps maintain vehicle braking action
and steering control.
The antilock CAB activates the system whenever
sensor signals indicate periods of high wheel slip.
High wheel slip can be described as the point where
wheel rotation begins approaching 20 to 30 percent of
actual vehicle speed during braking. Periods of high
wheel slip occur when brake stops involve high pedal
pressure and rate of vehicle deceleration.
The antilock system prevents lockup during high
slip conditions by modulating fluid apply pressure to
the wheel brake units.
Brake fluid apply pressure is modulated according
to wheel speed, degree of slip and rate of decelera-
tion. Sensors at each front wheel convert wheel speed
into electrical signals. These signals are transmitted
to the CAB for processing and determination of
wheel slip and deceleration rate.
The ABS system has three fluid pressure control
channels. The front brakes are controlled separately
and the rear brakes in tandem. A speed sensor input
signal indicating a high slip condition activates the
CAB antilock program.
Two solenoid valves are used in each antilock con-
trol channel. The valves are all located within the
HCU valve body and work in pairs to either increase,
hold, or decrease apply pressure as needed in the
individual control channels.
The solenoid valves are not static during antilock
braking. They are cycled continuously to modulate
pressure. Solenoid cycle time in antilock mode can be
measured in milliseconds.
CONTROLLER ANTILOCK BRAKES
DESCRIPTION
The CAB is mounted on the top of the hydraulic
control unit (Fig. 2). The CAB operates the ABS sys-
tem and is separate from other vehicle electrical cir-
cuits. CAB voltage source is through the ignition
switch in the RUN position.
OPERATION
The CAB contains dual microprocessors. A logic
block in each microprocessor receives identical sensor
signals. These signals are processed and compared
simultaneously.
The CAB contains a self check program that illu-
minates the ABS warning light when a system fault
is detected. Faults are stored in a diagnostic program
memory and are accessible with the DRB scan tool.
ABS faults remain in memory until cleared, or
until after the vehicle is started approximately 50
times. Stored faults are not erased if the battery is
disconnected.
NOTE: If the CAB needs to be replaced, the rear
axle type and tire revolutions per mile must be pro-
gramed into the new CAB. For axle type refer to
Group 3 Differential and Driveline. For tire revolu-
tions per mile refer to Group 22 Tire and Wheels. To
program the CAB refer to the Chassis Diagnostic
Manual.
HYDRAULIC CONTROL UNIT
DESCRIPTION
The hydraulic control unit (HCU) consists of a
valve body, pump, two accumulators and a motor
(Fig. 2). The assembly is mounted on the driverside
inner fender under the hood.
OPERATION
The pump, motor, and accumulators are combined
into an assembly attached to the valve body. The
accumulators store the extra fluid which had to be
dumped from the brakes. This is done to prevent the
wheels from locking up. The pump provides the fluid
volume needed and is operated by a DC type motor.
The motor is controlled by the CAB.
Fig. 2 CAB/HCU
1 – CAB
2 – PUMP WIRING
3 – PUMP MOTOR
4 – HCU
DN
BRAKES
5 - 41
DESCRIPTION AND OPERATION (Continued)
During normal braking, the HCU solenoid valves
and pump are not activated. The master cylinder and
power booster operate the same as a vehicle without
an ABS brake system.
The valve body contains the solenoid valves. The
valves modulate brake pressure during antilock brak-
ing and are controlled by the CAB.
The HCU provides three channel pressure control
to the front and rear brakes. One channel controls
the rear wheel brakes in tandem. The two remaining
channels control the front wheel brakes individually.
During antilock braking, the solenoid valves are
opened and closed as needed. The valves are not
static. They are cycled rapidly and continuously to
modulate pressure and control wheel slip and decel-
eration.
During antilock braking, solenoid valve pressure
modulation occurs in three stages, pressure decrease,
pressure hold, and pressure increase. The valves are
all contained in the valve body portion of the HCU.
PRESSURE DECREASE
The inlet valve is closed and the outlet valve is
opened during the pressure decrease cycle.
A pressure decrease cycle is initiated when speed
sensor signals indicate high wheel slip at one or
more wheels. At this point, the CAB closes the inlet
to prevent the driver from further increasing the
brake pressure and locking the brakes. The CAB
then opens the outlet valve, which also opens the
return circuit to the accumulators. Fluid pressure is
allowed to bleed off (decrease) as needed to prevent
wheel lock.
Once the period of high wheel slip has ended, the
CAB closes the outlet valve and begins a pressure
increase or hold cycle as needed.
PRESSURE HOLD
Both solenoid valves are closed in the pressure
hold cycle. Fluid apply pressure in the control chan-
nel is maintained at a constant rate. The CAB main-
tains the hold cycle until sensor inputs indicate a
pressure change is necessary.
PRESSURE INCREASE
The inlet valve is open and the outlet valve is
closed during the pressure increase cycle. The pres-
sure increase cycle is used to counteract unequal
wheel speeds. This cycle controls re-application of
fluid apply pressure due to changing road surfaces or
wheel speed.
WHEEL SPEED SENSOR
DESCRIPTION
The ABS brake system uses 3 wheel speed sensors.
A sensor is mounted to each front steering knuckles.
The third sensor is mounted on top of the rear axle
differential housing.
OPERATION
The WSS consists of a magnet surrounded by
windings from a single strand of wire. The sensor
sends a small AC signal to the CAB. This signal is
generated by magnetic induction. The magnetic
induction is created when a toothed sensor ring
(exciter ring or tone wheel) passes the stationary
magnetic WSS.
When the ring gear is rotated, the exciter ring
passes the tip of the WSS. As the exciter ring tooth
approaches the tip of the WSS, the magnetic lines of
force expand, causing the magnetic field to cut across
the sensor’s windings. This, in turn causes current to
flow through the WSS circuit (Fig. 3) in one direc-
tion. When the exciter ring tooth moves away from
the sensor tip, the magnetic lines of force collapse
cutting the winding in the opposite direction. This
causes the current to flow in the opposite direction.
Every time a tooth of the exciter ring passes the tip
of the WSS, an AC signal is generated. Each AC sig-
nal (positive to negative signal or sinewave) is inter-
preted by the CAB. It then compares the frequency of
the sinewave to a time value to calculate vehicle
speed. The CAB continues to monitor the frequency
to determine a deceleration rate that would indicate
a possible wheel-locking tendency.
The signal strength of any magnetic induction sen-
sor is directly affected by:
• Magnetic field strength; the stronger the mag-
netic field, the stronger the signal
• Number of windings in the sensor; more wind-
ings provide a stronger signal
• Exciter ring speed; the faster the exciter ring/
tone wheel rotates, the stronger the signal will be
• Distance between the exciter ring teeth and
WSS; the closer the WSS is to the exciter ring/tone
wheel, the stronger the signal will be
The rear WSS is not adjustable. A clearance speci-
fication has been established for manufacturing toler-
ances.
If
the
clearance
is
not
within
these
specifications, then either the WSS or other compo-
nents may be damaged. The clearance between the
WSS and the exciter ring is 0.005 – 0.050 in.
5 - 42
BRAKES
DN
DESCRIPTION AND OPERATION (Continued)
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