2005 CHRYSLER VOYAGER Rear system

BRAKES - ABS
TABLE OF CONTENTS
page page
BRAKES - ABS
DESCRIPTION
DESCRIPTION - ANTILOCK BRAKE
SYSTEM............................87
DESCRIPTION - ANTILOCK BRAKE
SYSTEM (EXPORT)....................87
DESCRIPTION - ELECTRONIC VARIABLE
BRAKE PROPORTIONING...............88
DESCRIPTION - TRACTION CONTROL
SYSTEM............................88
OPERATION
OPERATION - ANTILOCK BRAKE SYSTEM . . 88
OPERATION - ELECTRONIC VARIABLE
BRAKE PROPORTIONING...............89
OPERATION - TRACTION CONTROL
SYSTEM............................89
CAUTION.............................90
STANDARD PROCEDURE - ANTILOCK BRAKE
SYSTEM BLEEDING...................90
SPECIFICATIONS
ABS FASTENER TORQUE...............91
TONE WHEEL RUNOUT................91
WHEEL SPEED SENSOR AIR GAP........91
FRONT WHEEL SPEED SENSOR
REMOVAL.............................91
INSTALLATION.........................92
REAR WHEEL SPEED SENSOR - AWD
REMOVAL.............................92INSTALLATION.........................92
REAR WHEEL SPEED SENSOR - FWD
REMOVAL.............................93
INSTALLATION.........................93
TONE WHEEL
INSPECTION - TONE WHEEL..............94
TRACTION CONTROL SWITCH
DIAGNOSIS AND TESTING - TRACTION
CONTROL SWITCH....................94
REMOVAL.............................95
INSTALLATION.........................95
HYDRAULIC/MECHANICAL
OPERATION - HYDRAULIC CIRCUITS AND
VALVES .............................95
HCU (HYDRAULIC CONTROL UNIT)
DESCRIPTION........................100
OPERATION..........................101
ICU (INTEGRATED CONTROL UNIT)
DESCRIPTION........................102
OPERATION..........................102
REMOVAL
REMOVAL - LHD.....................102
REMOVAL - RHD.....................104
DISASSEMBLY - ICU...................105
ASSEMBLY - ICU......................106
INSTALLATION
INSTALLATION - LHD.................106
INSTALLATION - RHD.................107
BRAKES - ABS
DESCRIPTION
DESCRIPTION - ANTILOCK BRAKE SYSTEM
This section covers the physical and operational
descriptions and the on-car service procedures for the
Mark 20e Antilock Brake System and the Mark 20e
Antilock Brake System with traction control.
The purpose of the antilock brake system (ABS) is
to prevent wheel lockup under braking conditions on
virtually any type of road surface. Antilock braking is
desirable because a vehicle that is stopped without
locking the wheels retains directional stability and
some steering capability. This allows the driver to
retain greater control of the vehicle during braking.
DESCRIPTION - ANTILOCK BRAKE SYSTEM
(EXPORT)
Four-wheel disc antilock brakes are standard on all
models. The Mark 20e antilock brake system is used
on all models. Depending on whether the vehicle is a
left-hand drive (LHD) or right-hand drive (RHD)
model, the integrated control unit (ICU) is located in
one of two locations. On LHD models, the ICU is
mounted above the front suspension cradle/cross-
member below the master cylinder. On RHD models,
the ICU is located behind the front suspension cra-
dle/crossmember on the left side of the vehicle.
RSBRAKES - ABS5-87

DESCRIPTION - ELECTRONIC VARIABLE
BRAKE PROPORTIONING
Vehicles equipped with ABS use electronic variable
brake proportioning (EVBP) to balance front-to-rear
braking. The EVBP is used in place of a rear propor-
tioning valve. The EVBP system uses the ABS system
to control the slip of the rear wheels in partial brak-
ing range. The braking force of the rear wheels is con-
trolled electronically by using the inlet and outlet
valves located in the integrated control unit (ICU).
EVBP activation is invisible to the customer since
there is no pump motor noise or brake pedal feedback.
DESCRIPTION - TRACTION CONTROL SYSTEM
Traction control reduces wheel slip and maintains
traction at the driving wheels at speeds below 56
km/h (35 mph) when road surfaces are slippery. The
traction control system reduces wheel slip by braking
the wheel that is losing traction.
HYDRAULIC SHUTTLE VALVES
Two pressure relief hydraulic shuttle valves are
included on vehicles with traction control. These
valves are located inside the HCU and cannot be ser-
viced separately from the HCU.
TRACTION CONTROL LAMP
The traction control function lamp is located in the
transmission range indicator display of the instru-
ment cluster, displaying TRAC, TRAC OFF or nei-
ther depending on system mode.
The TRAC OFF lamp is controlled by a Traction
Control Off switch that is a momentary contact type
switch. The Traction Control Off switch is located on
the steering column upper shroud.
OPERATION
OPERATION - ANTILOCK BRAKE SYSTEM
There are a few performance characteristics of the
Mark 20e Antilock Brake System that may at first
seem abnormal, but in fact are normal. These char-
acteristics are described below.
NORMAL BRAKING
Under normal braking conditions, the ABS func-
tions the same as a standard base brake system with
a diagonally split master cylinder and conventional
vacuum assist.
ABS BRAKING
ABS operation is available at all vehicle speeds above
3±5 mph. If a wheel locking tendency is detected during
a brake application, the brake system enters the ABS
mode. During ABS braking, hydraulic pressure in thefour wheel circuits is modulated to prevent any wheel
from locking. Each wheel circuit is designed with a set of
electric solenoids to allow modulation, although for vehi-
cle stability, both rear wheel solenoids receive the same
electrical signal. Wheel lockup may be perceived at the
very end of an ABS stop and is considered normal.
During an ABS stop, the brakes hydraulic system
is still diagonally split. However, the brake system
pressure is further split into three control channels.
During antilock operation of the vehicle's brake sys-
tem, the front wheels are controlled independently
and are on two separate control channels, and the
rear wheels of the vehicle are controlled together.
The system can build and release pressure at each
wheel, depending on signals generated by the wheel
speed sensors (WSS) at each wheel and received at
the controller antilock brake (CAB).
NOISE AND BRAKE PEDAL FEEL
During ABS braking, some brake pedal movement
may be felt. In addition, ABS braking will create
ticking, popping, or groaning noises heard by the
driver. This is normal and is due to pressurized fluid
being transferred between the master cylinder and
the brakes. If ABS operation occurs during hard
braking, some pulsation may be felt in the vehicle
body due to fore and aft movement of the suspension
as brake pressures are modulated.
At the end of an ABS stop, ABS is turned off when
the vehicle is slowed to a speed of 3±4 mph. There may
be a slight brake pedal drop anytime that the ABS is
deactivated, such as at the end of the stop when the
vehicle speed is less than 3 mph or during an ABS stop
where ABS is no longer required. These conditions exist
when a vehicle is being stopped on a road surface with
patches of ice, loose gravel, or sand on it. Also, stopping
a vehicle on a bumpy road surface activates ABS
because of the wheel hop caused by the bumps.
TIRE NOISE AND MARKS
Although the ABS system prevents complete wheel
lockup, some wheel slip is desired in order to achieve
optimum braking performance. Wheel slip is defined
as follows: 0 percent slip means the wheel is rolling
freely and 100 percent slip means the wheel is fully
locked. During brake pressure modulation, wheel slip
is allowed to reach up to 25±30 percent. This means
that the wheel rolling velocity is 25±30 percent less
than that of a free rolling wheel at a given vehicle
speed. This slip may result in some tire chirping,
depending on the road surface. This sound should not
be interpreted as total wheel lockup.
Complete wheel lockup normally leaves black tire
marks on dry pavement. The ABS will not leave dark
black tire marks since the wheel never reaches a
fully locked condition. However, tire marks may be
noticeable as light patched marks.
5 - 88 BRAKES - ABSRS
BRAKES - ABS (Continued)

START-UP CYCLE
When the ignition is turned on, a popping sound
and a slight brake pedal movement may be noticed.
The ABS warning lamp will also be on for up to 5
seconds after the ignition is turned on. When the
vehicle is first driven off, a humming may be heard
or felt by the driver at approximately 20±40 kph
(12±25 mph). All of these conditions are a normal
function of ABS as the system is performing a diag-
nosis check.
PREMATURE ABS CYCLING
Symptoms of premature ABS cycling include: click-
ing sounds from the solenoid valves; pump/motor
running; and pulsations in the brake pedal. Prema-
ture ABS cycling can occur at any braking rate of the
vehicle and on any type of road surface. Neither the
red BRAKE warning lamp, nor the amber ABS warn-
ing lamp, illuminate and no fault codes are stored in
the CAB.
Premature ABS cycling is a condition that needs to
be correctly assessed when diagnosing problems with
the antilock brake system. It may be necessary to use
a DRB scan tool to detect and verify premature ABS
cycling.
Check the following common causes when diagnos-
ing premature ABS cycling: damaged tone wheels;
incorrect tone wheels; damaged steering knuckle
wheel speed sensor mounting bosses; loose wheel
speed sensor mounting bolts; excessive tone wheel
runout; or an excessively large tone wheel-to-wheel
speed sensor air gap. Give special attention to these
components when diagnosing a vehicle exhibiting
premature ABS cycling.
After diagnosing the defective component, repair or
replace it as required. When the component repair or
replacement is completed, test drive the vehicle to
verify that premature ABS cycling has been cor-
rected.
OPERATION - ELECTRONIC VARIABLE BRAKE
PROPORTIONING
Upon entry into EVBP the inlet valve for the rear
brake circuit is switched on so that the fluid supply
from the master cylinder is shut off. In order to
decrease the rear brake pressure, the outlet valve for
the rear brake circuit is pulsed. This allows fluid to
enter the low pressure accumulator (LPA) in the
hydraulic control unit (HCU) resulting in a drop in
fluid pressure to the rear brakes. In order to increase
the rear brake pressure, the outlet valve is switched
off and the inlet valve is pulsed. This increases the
pressure to the rear brakes. This back-and-forth pro-
cess will continue until the required slip difference is
obtained. At the end of EVBP braking (brakes
released) the fluid in the LPA drains back to themaster cylinder by switching on the outlet valve and
draining through the inlet valve check valve. At the
same time the inlet valve is switched on in case of
another brake application.
The EVBP will remain functional during many
ABS fault modes. If both the red BRAKE and amber
ABS warning indicators are illuminated, the EVBP
may not be functioning.
OPERATION - TRACTION CONTROL SYSTEM
The traction control module monitors wheel speed.
During acceleration, if the module detects front
(drive) wheel slip and the brakes are not applied, the
module enters traction control mode. Traction control
operation proceeds in the following order:
(1) Close the normally open isolation valves.
(2) Start the pump/motor and supply volume and
pressure to the front (drive) hydraulic circuit. (The
pump/motor runs continuously during traction con-
trol operation.)
(3) Open and close the build and decay valves to
maintain minimum wheel slip and maximum trac-
tion.
The cycling of the build and decay valves during
traction control is similar to that during antilock
braking, except the valves work to control wheel spin
by applying the brakes, whereas the ABS function is
to control wheel skid by releasing the brakes.
If the brakes are applied at anytime during a trac-
tion control cycle, the brake lamp switch triggers the
controller to switch off traction control.
HYDRAULIC SHUTTLE VALVES
Two pressure relief hydraulic shuttle valves allow
pressure and volume to return to the master cylinder
reservoir when not consumed by the build and decay
valves. These valves are necessary because the
pump/motor supplies more volume than the system
requires.
TRACTION CONTROL LAMP
The traction control system is enabled at each igni-
tion cycle. It may be turned off by depressing the
Traction Control Off switch button when the ignition
is in the ON position. The traction control function
lamp (TRAC OFF) illuminates immediately upon
depressing the button.
The traction control function lamp illuminates dur-
ing a traction control cycle, displaying TRAC.
If the CAB calculates that the brake temperatures
are high, the traction control system becomes inoper-
ative until a time-out period has elapsed. During this
ªthermo-protection mode,º the traction control func-
tion lamp illuminates TRAC OFF; note that no trou-
ble code is registered.
RSBRAKES - ABS5-89
BRAKES - ABS (Continued)

(1) Make sure all hydraulic fluid lines are installed
and properly torqued.
(2) Connect the DRBIIItscan tool to the diagnos-
tics connector. The diagnostic connector is located
under the lower steering column cover to the left of
the steering column.
(3) Using the DRB, check to make sure the CAB
does not have any fault codes stored. If it does, clear
them using the DRB.
WARNING: WHEN BLEEDING THE BRAKE SYSTEM
WEAR SAFETY GLASSES. A CLEAR BLEED TUBE
MUST BE ATTACHED TO THE BLEEDER SCREWS
AND SUBMERGED IN A CLEAR CONTAINER FILLED
PART WAY WITH CLEAN BRAKE FLUID. DIRECT
THE FLOW OF BRAKE FLUID AWAY FROM YOUR-
SELF AND THE PAINTED SURFACES OF THE VEHI-
CLE. BRAKE FLUID AT HIGH PRESSURE MAY
COME OUT OF THE BLEEDER SCREWS WHEN
OPENED.
(4) Bleed the base brake system using the stan-
dard pressure or manual bleeding procedure. (Refer
to 5 - BRAKES - BASE - STANDARD PROCEDURE)
(5) Using the DRB, select ANTILOCK BRAKES,
followed by MISCELLANEOUS, then BLEED
BRAKES. Follow the instructions displayed. When
the scan tool displays TEST COMPLETED, discon-
nect the scan tool and proceed.
(6) Bleed the base brake system a second time.
Check brake fluid level in the reservoir periodically
to prevent emptying, causing air to enter the hydrau-
lic system.
(7) Fill the master cylinder reservoir to the full
level.
(8) Test drive the vehicle to be sure the brakes are
operating correctly and that the brake pedal does not
feel spongy.
SPECIFICATIONS
ABS FASTENER TORQUE
Refer to BRAKE FASTENER TORQUE. (Refer to 5
- BRAKES - BASE - SPECIFICATIONS)
TONE WHEEL RUNOUT
DESCRIPTION SPECIFICATION
Front Tone Wheel
Maximum Runout0.15 mm (0.006 in.)
Rear Tone Wheel
Maximum Runout0.15 mm (0.006 in.)
WHEEL SPEED SENSOR AIR GAP
DESCRIPTION SPECIFICATION
Front Sensor0.35 ± 1.20 mm
0.014 ± 0.047 in.
Rear Sensor0.40 ± 1.20 mm
0.016 ± 0.047 in.
FRONT WHEEL SPEED
SENSOR
REMOVAL
(1)Raise vehicle. (Refer to LUBRICATION & MAIN-
TENANCE/HOISTING - STANDARD PROCEDURE)
(2) Remove the tire and wheel assembly.
(3) Remove the sensor cable routing clamp screws.
CAUTION: When disconnecting the wheel speed
sensor from vehicle wiring harness, be careful not
to damage pins on connector
(4) Remove speed sensor cable grommets from
intermediate bracket on strut.
(5) Disconnect speed sensor cable from vehicle wir-
ing harness behind fender well shield.
(6) Remove the wheel speed sensor head mounting
bolt (Fig. 1).
(7) Remove sensor head from steering knuckle. If
sensor has seized due to corrosion,DO NOT USE
PLIERS ON SENSOR HEAD.Use a hammer and a
punch and tap edge of sensor ear, rocking the sensor
side-to-side until free.
Fig. 1 Front Wheel Speed Sensor Attaching Bolt
1 - MOUNTING BOLT
2 - WHEEL SPEED SENSOR
3 - DRIVESHAFT
4 - TONE WHEEL
5 - STEERING KNUCKLE
RSBRAKES - ABS5-91
BRAKES - ABS (Continued)

(8) Remove front wheel speed sensor from vehicle.
INSTALLATION
CAUTION: Proper installation of wheel speed sen-
sor cables is critical to continued system operation.
Be sure that cables are installed in retainers. Fail-
ure to install cables in retainers as shown in this
section may result in contact with moving parts and
over extension of cables, resulting in an open cir-
cuit.
(1) Connect the front wheel speed sensor cable to
the vehicle wiring harness connector. Be sure speed
sensor cable connector is fully seated and locked into
vehicle wiring harness connector.
(2) Install the bolts attaching the routing clamps
to the body of the vehicle. Tighten the bolts to a
torque of 14 N´m (125 in. lbs.).
(3) Insert speed sensor cable grommets into inter-
mediate bracket on strut.
(4) Install the wheel speed sensor head mounting
bolt (Fig. 1). Tighten the bolt to a torque of 13 N´m
(115 in. lbs.)
(5) Install the wheel and tire assembly on vehicle.
(6) Lower vehicle.
(7) Road test vehicle to ensure proper operation of
the base and ABS brake systems.
REAR WHEEL SPEED SENSOR
-AWD
REMOVAL
(1) Raise vehicle. (Refer to LUBRICATION &
MAINTENANCE/HOISTING - STANDARD PROCE-
DURE)
CAUTION: When disconnecting speed sensor cable
from vehicle wiring harness be careful not to dam-
age pins on the electrical connectors. Also, inspect
connectors for any signs of previous damage.
(2) Remove grommet from floor pan of vehicle and
disconnect speed sensor cable connector from vehicle
wiring harness.
CAUTION: When removing rear wheel speed sensor
cable from routing clips, be sure not to damage the
routing clips. Routing clips that are molded onto
the brake hose will require replacement of the brake
hose if damaged during removal or installation of
the speed sensor cable.
(3) Carefully remove speed sensor cable from
press-in routing clips along brake hose and tubing.(4) Remove bolt securing wheel speed sensor cable
metal clip to rear of axle. Remove metal clip from
cable if necessary.
CAUTION: If speed sensor head has seized due to
corrosion, do not use pliers on speed sensor head
in an attempt to remove it. Use a hammer and a
punch and tap mounting flange edge side-to-side,
rocking the sensor until free.
(5) Remove wheel speed sensor head attaching
bolt.
(6) Remove wheel speed sensor head from the axle,
and remove sensor from vehicle.
INSTALLATION
CAUTION: Proper installation of wheel speed sen-
sor cables is critical to continued system operation.
Be sure that cables are installed in retainers. Fail-
ure to install cables in retainers as indicated may
result in contact with moving parts or over-exten-
sion of cables, resulting in an open circuit.
(1) Install wheel speed sensor head in axle flange.
CAUTION: Prior to installing the speed sensor head
attaching bolt, the plastic anti-rotation pin must be
fully seated into the bearing flange.
(2) Install wheel speed sensor head attaching bolt.
Tighten bolt to a torque 10 N´m (90 in. lbs.).
(3) Check the air gap between the face of the
wheel speed sensor and the top surface of the tone
wheel. (Refer to 5 - BRAKES - SPECIFICATIONS)
CAUTION: When installing wheel speed sensor
cable in the routing clips on rear brake flex hose,
be sure not to damage the routing clips. Routing
clips are molded onto the hose and will require
replacement of the brake hose if damaged.
(4) Install speed sensor cable under leaf spring
onto brake hose and tubing utilizing routing clips to
secure it in place.
(5) Install metal routing clip on speed sensor cable
and mount it to rear of axle with mounting bolt.
Tighten mounting bolt to 16 N´m (140 in. lbs.).
(6) Connect wheel speed sensor cable to vehicle
wiring harness.Be sure speed sensor cable con-
nector is fully seated and locked into vehicle
wiring harness connector.
(7) Install speed sensor cable grommet into the
floor pan, being sure the grommet is fully seated into
the access hole.
(8) Lower vehicle.
(9) Road test vehicle to ensure proper operation of
the base and ABS braking systems.
5 - 92 BRAKES - ABSRS
FRONT WHEEL SPEED SENSOR (Continued)

REAR WHEEL SPEED SENSOR
- FWD
REMOVAL
(1) Raise vehicle. (Refer to LUBRICATION &
MAINTENANCE/HOISTING - STANDARD PROCE-
DURE)
CAUTION: When disconnecting speed sensor cable
from vehicle wiring harness be careful not to dam-
age pins on the electrical connectors. Also, inspect
connectors for any signs of previous damage.
(2) Remove grommet from floor pan of vehicle and
disconnect speed sensor cable connector from vehicle
wiring harness (Fig. 2).
CAUTION: When removing rear wheel speed sensor
cable from routing clips, be sure not to damage the
routing clips. Routing clips that are molded onto
the brake hose will require replacement of the brake
hose if damaged during removal or installation of
the speed sensor cable.
(3) Carefully remove speed sensor cable from
press-in routing clips (Fig. 3).
(4) Remove bolt securing metal routing clip to rear
of axle and remove sensor cable from metal clip (Fig.
3).
(5) Remove secondary (yellow) retaining clip at
rear of wheel speed sensor head (Fig. 4).
(6) Push up on metal retaining clip (Fig. 4) until it
bottoms. This will release wheel speed sensor head
from hub and bearing. While holding metal clip up,
pull back on wheel speed sensor head removing it
from hub and bearing.(7) Remove wheel speed sensor assembly from
vehicle.
INSTALLATION
CAUTION: Proper installation of wheel speed sen-
sor cable is critical to continued system operation.
Be sure that cable is installed in routing retainers/
clips. Failure to install cable in retainers may result
in contact with moving parts or over extension of
cable, resulting in an open circuit.
CAUTION: It is important that only MoparTWheel
Bearing Grease be used for the following step appli-
cation. Other lubricants may cause sensor failure.
Fig. 2 Wheel Speed Sensor Connector
1 - CONNECTOR
2 - FLOOR PAN
3 - GROMMET
Fig. 3 SPEED SENSOR CABLE ROUTING
1 - METAL CLIP AND MOUNTING BOLT
2 - ROUTING CLIPS
Fig. 4 SENSOR CONNECTION AT HUB AND
BEARING
1 - SECONDARY SENSOR RETAINING CLIP
2 - METAL SENSOR RETAINING CLIP
3 - HUB AND BEARING
RSBRAKES - ABS5-93

(1) Lubricate the sensor O-ring with Mopar Wheel
Bearing Grease before installation into the Hub And
Bearing.If not lubricated, an improper seal may
result due to rolling of the O-ring.
(2) If metal sensor retaining clip is not in the neu-
tral installed position on hub and bearing cap, install
from the bottom, if necessary, and push clip upward
until it snaps into position.
(3) Install wheel speed sensor head into rear of
hub and bearing aligning index tab with the notch in
the top of the mounting hole. Push the sensor in
until it snaps into place on the metal retaining clip.
(4)
Install secondary (yellow) retaining clip over wheel
speed sensor head and engage the tabs on each side.
(5) Route sensor cable under leaf spring along rear
of axle. Install speed sensor cable into routing clips
on rear brake flex hose (Fig. 3).
(6) Install cable into metal routing clip and attach
it to the rear axle with mounting bolt (Fig. 3).
Tighten mounting bolt to 16 N´m (140 in. lbs.).
(7) Connect wheel speed sensor cable to vehicle
wiring harness (Fig. 2).Be sure speed sensor
cable connector is fully seated and locked into
vehicle wiring harness connector.
(8)
Install speed sensor cable grommet into hole in
floor pan making sure grommet is fully seated into hole.
(9) Lower vehicle.
(10) Road test vehicle to ensure proper operation
of the base and ABS braking systems.
TONE WHEEL
INSPECTION - TONE WHEEL
NOTE: Rear tone wheels for front-wheel-drive vehi-
cles are sealed within the hub and bearing assem-
bly and cannot be inspected or replaced.
Replacement of the hub and bearing is necessary.
Tone wheels can cause erratic wheel speed sensor
signals. Inspect tone wheels for the following possible
causes.
²missing, chipped, or broken teeth
²contact with the wheel speed sensor
²wheel speed sensor to tone wheel alignment
²wheel speed sensor to tone wheel clearance
²excessive tone wheel runout
²tone wheel loose on its mounting surface
If a front tone wheel is found to need replacement,
the drive shaft must be replaced. No attempt should
be made to replace just the tone wheel. (Refer to 3 -
DIFFERENTIAL & DRIVELINE/HALF SHAFT -
REMOVAL)
If a rear tone wheel is found to need replacement
on an all-wheel-drive model, the drive shaft must be
replaced. No attempt should be made to replace justthe tone wheel. (Refer to 3 - DIFFERENTIAL &
DRIVELINE/HALF SHAFT - REMOVAL)
If wheel speed sensor to tone wheel contact is evi-
dent, determine the cause and correct it before
replacing the wheel speed sensor or tone wheel.
Check the gap between the speed sensor head and
the tone wheel to ensure it is within specifications.
(Refer to 5 - BRAKES - ABS/ELECTRICAL - SPEC-
IFICATIONS)
Excessive wheel speed sensor runout can cause
erratic wheel speed sensor signals. Refer to SPECI-
FICATIONS in this section of the service manual for
the maximum allowed tone wheel runout (Refer to 5 -
BRAKES - ABS/ELECTRICAL - SPECIFICATIONS).
If tone wheel runout is excessive, determine if it is
caused by a defect in the driveshaft assembly or hub
and bearing. Replace as necessary.
Tone wheels are pressed onto their mounting sur-
faces and should not rotate independently from the
mounting surface. Replacement of the front drive-
shaft, rear driveshaft (AWD only) or rear hub and
bearing is necessary.
TRACTION CONTROL SWITCH
DIAGNOSIS AND TESTING - TRACTION
CONTROL SWITCH
(1) Remove lower steering column shroud. (Refer
to 19 - STEERING/COLUMN/LOWER SHROUD -
REMOVAL)
Fig. 5 Traction Control And Autostick Wiring
Connections
1 - TRACTION CONTROL WIRING CONNECTOR
2 - ROUTING CLIP
3 - AUTOSTICK WIRING CONNECTOR
4 - COLUMN WIRING HARNESS
5 - 94 BRAKES - ABSRS
REAR WHEEL SPEED SENSOR - FWD (Continued)

For more information, (Refer to 5 - BRAKES/HY-
DRAULIC/MECHANICAL/ICU (INTEGRATED CON-
TROL UNIT) - DESCRIPTION)
OPERATION
For information on the operation of the HCU as a
whole, refer to Hydraulic Circuits And Valve Opera-
tion which can be found elsewhere in this section.
For information on the operation of the components
within the HCU, refer to the following three topics.
VALVES AND SOLENOIDS
The valve block contains four inlet valves and four
outlet valves. The inlet valves are spring-loaded in
the open position and the outlet valves are spring-
loaded in the closed position during normal braking.
The fluid is allowed to flow from the master cylinder
to the wheel brakes.
During an ABS stop, these valves cycle to maintain
the proper slip ratio for each wheel. The inlet valve
closes preventing further pressure increase and the
outlet valve opens to provide a path from the wheel
brake to the HCU accumulators and pump/motor.
This releases (decays) pressure from the wheel brake,
thus releasing the wheel from excessive slippage.
Once the wheel is no longer slipping, the outlet valve
is closed and the inlet valve is opened to reapply
(build) pressure.
On vehicles with traction control, there is an extra
set of valves and solenoids. The ASR valves, mounted
in the HCU valve block, are normally in the open
position and close only when the traction control is
applied.
These isolator valves are used to isolate the rear
(non-driving) wheels of the vehicle from the hydraulic
pressure that the HCU pump/motor is sending to the
front (driving) wheels when traction control is being
applied. The rear brakes need to be isolated from the
master cylinder when traction control is being
applied so the rear wheels do not drag. For more
information, refer to Traction Control System in this
section.
BRAKE FLUID ACCUMULATORS
There are two fluid accumulators in the HCU±one
for the primary hydraulic circuit and one for the sec-
ondary hydraulic circuit. Each hydraulic circuit uses
a 5 cc accumulator.
The fluid accumulators temporarily store brake
fluid that is removed from the wheel brakes during
an ABS cycle. This stored fluid is used by the pump/
motor to provide build pressure for the brake hydrau-
lic system. When the antilock stop is complete, the
accumulators are drained by the pump/motor.
On ABS-only vehicles, there is a mini-accumulator
on the secondary hydraulic circuit that protects the
master cylinder seals during an ABS stop, and there
is a noise dampening chamber on the primary circuit.
On ABS with traction control vehicles, there are
two noise dampening chambers in the HCU.
PUMP/MOTOR
There are two pump assemblies in the HCUÐone
for the primary hydraulic circuit and one for the sec-
ondary hydraulic circuit. Both pumps are driven by a
common electric motor. This DC-type motor is inte-
gral to the HCU and is controlled by the CAB.
The pump/motor provides the extra amount of
brake fluid needed during antilock braking. Brake
fluid is released to the accumulators when the outlet
valve is opened during an antilock stop. The pump
mechanism consists of two opposing pistons operated
by an eccentric camshaft. In operation, one piston
draws fluid from the accumulators, and the opposing
piston pumps fluid to the master cylinder circuits.
When the antilock stop is complete, the pump/motor
drains the accumulators.
The CAB may turn on the pump/motor when an
antilock stop is detected. The pump/motor continues
to run during the antilock stop and is turned off after
the stop is complete. Under some conditions, the
pump/motor runs to drain the accumulators during
the next drive-off.
The pump/motor is not a serviceable item; if it
requires replacement, the HCU must be replaced.
RSBRAKES - ABS5 - 101
HCU (HYDRAULIC CONTROL UNIT) (Continued)