traction control CHRYSLER CARAVAN 2003 Service Manual
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REAR DRIVELINE MODULE
TABLE OF CONTENTS
page page
REAR DRIVELINE MODULE
DESCRIPTION.........................23
OPERATION...........................23
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - REAR
DRIVELINE MODULE NOISE.............24
DIAGNOSIS AND TESTING - REAR
DRIVELINE MODULE OPERATION........26
REMOVAL.............................26
DISASSEMBLY.........................27
ASSEMBLY............................29
INSTALLATION.........................33
SPECIFICATIONS - REAR DRIVELINE
MODULE............................34
SPECIAL TOOLS.......................34
BI-DIRECTIONAL OVERRUNNING CLUTCH
DESCRIPTION.........................34
OPERATION...........................36
DIFFERENTIAL ASSEMBLY
DESCRIPTION.........................39OPERATION...........................39
FLUID - DIFFERENTIAL ASSEMBLY
STANDARD PROCEDURE - DIFFERENTIAL
ASSEMBLY FLUID CHANGE.............40
FLUID - OVERRUNNING CLUTCH HOUSING
STANDARD PROCEDURE - OVERRUNNING
CLUTCH HOUSING FLUID CHANGE.......41
VISCOUS COUPLER
DESCRIPTION.........................41
OPERATION...........................42
TORQUE ARM
REMOVAL.............................44
INSTALLATION.........................44
INPUT FLANGE SEAL
REMOVAL.............................44
INSTALLATION.........................45
OUTPUT FLANGE SEAL
REMOVAL.............................45
INSTALLATION.........................46
REAR DRIVELINE MODULE
DESCRIPTION
The rear driveline module assembly (Fig. 1) con-
sists of four main components:
²Bi-Directional Overrunning Clutch (BOC)
²Viscous Coupling
²Differential Assembly
²Torque Arm
The viscous coupling and bi-directional overrun-
ning clutch are contained within an overrunning
clutch housing, which fastens to the differential
assembly. The overrunning clutch housing and differ-
ential assembly have unique fluid sumps, each
requiring their own type and capacity of fluid. The
overrunning clutch housing requires MopartATF+4
(Automatic Transmission FluidÐType 9602) or equiv-
alent. The differential assembly requires Mopart
80W-90 Gear and Axle Lubricant.
Driveline module service is limited to the following
components:
²Differential Assembly (serviced only as assem-
bly)
²Viscous Coupling
²Bi-Directional Overrunning Clutch (BOC)
²Overrunning Clutch Housing²Seals (Input Flange, Output Flange, Overrun-
ning Clutch Housing O-rings)
²Input Flange/Shield
²Torque Arm
²Vents
²Fasteners
OPERATION
The primary benefits of All Wheel Drive are:
²Superior straight line acceleration, and corner-
ing on all surfaces
²Better traction and handling under adverse con-
ditions, resulting in improved hill climbing ability
and safer driving.
The heart of the system is an inter-axle viscous
coupling. The vehicle retains predominantly front-
wheel drive characteristics, but the All Wheel Drive
capability takes effect when the front wheels start to
slip. Under normal level road, straight line driving,
100% of the torque is allocated to the front wheels.
The viscous coupling controls and distributes torque/
power to the rear wheels. The viscous coupling trans-
mits torque to the rear wheels in proportion of the
amount of the slippage at the front wheels. Thais
variable torque distribution is automatic with no
driver inputs required. The coupling is similar to a
multi-plate clutch. It consists of a series of closely
spaced discs, which are alternately connected to the
RSREAR DRIVELINE MODULE3-23
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Page 141 of 2177
torque to the rear wheels in accordance with the
amount of slippage at the front wheels. The variable
torque distribution is automatic with no driver
inputs required.
OPERATION
The viscous coupler (Fig. 46) is a housing nearly
filled with a high viscosity silicone liquid and thin
metal plates alternately splined to an inner and
outer drum. The viscous coupler provides torque in
the following modes:²Shear mode (normal operation)
²Hump mode (locked mode)
The inner plates are slotted around the radius and
the outer plates have holes in them. In the shear
mode (normal operation), the plates are evenly
spaced and the torque is created by the shearing of
the plates through the fluid and 90-100% of the
torque is applied to the rear axle. During the shear
mode, a fluid flow pattern is created from this design
(holes and slots). This fluid flow causes high pressure
on each side of each pair of plates and low pressure
between each pair of plates.
When a high speed difference (shear) occurs
because of loss of traction (one axle spinning faster
than the other), the silicone fluid expands as it heats
from this shearing. When the silicone expands to fill
the viscous coupler completely, this pressure differ-
ence is high enough to squeeze each pair of plates
together. The resulting hump torque is up to 8 times
higher than the shear torque. When the viscous cou-
pler is in the hump mode, it does not lock the axles
(undifferentiated 4-Wheel Drive). It controls the
amount of slippage while delivering maximum power
to the axle having greatest traction. Once the speed
difference equalizes the fluid and plates cool down
and the viscous coupler goes back to the shear mode.
Fig. 45 Filling Overrunning Clutch Case
1 - OVERRUNNING CLUTCH HOUSING FILL HOLE
2 - SUCTION GUN
3 - 42 REAR DRIVELINE MODULERS
VISCOUS COUPLER (Continued)
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CABLES - PARKING BRAKE
REMOVAL
REMOVAL - PARKING BRAKE CABLE
(FRONT)............................59
REMOVAL - PARKING BRAKE CABLE
(INTERMEDIATE)......................60
REMOVAL - PARKING BRAKE CABLE
(RIGHT REAR)........................60
REMOVAL - PARKING BRAKE CABLE (LEFT
REAR)..............................62
INSTALLATION
INSTALLATION - PARKING BRAKE CABLE
(FRONT)............................63
INSTALLATION - PARKING BRAKE CABLE
(INTERMEDIATE)......................63
INSTALLATION - PARKING BRAKE CABLE
(RIGHT REAR)........................63
INSTALLATION - PARKING BRAKE CABLE
(LEFT REAR).........................64ADJUSTMENTS
ADJUSTMENT - PARKING BRAKE CABLES . 64
CABLES - PARKING BRAKE (EXPORT)
REMOVAL - FRONT CABLE...............64
INSTALLATION - FRONT CABLE............64
LEVER - PARKING BRAKE
REMOVAL.............................64
INSTALLATION.........................65
LEVER - PARKING BRAKE (EXPORT)
REMOVAL - PARKING BRAKE LEVER AND
FRONT CABLE.......................65
INSTALLATION - PARKING BRAKE LEVER
AND FRONT CABLE...................66
SHOES - PARKING BRAKE
REMOVAL.............................67
INSTALLATION.........................72
ADJUSTMENTS
ADJUSTMENT - PARKING BRAKE SHOES . . 73
BRAKES - BASE
DESCRIPTION
DESCRIPTION - BASE BRAKES
The base brake system consists of the following
components:
²Brake pedal
²Power brake booster
²Master cylinder
²Brake tubes and hoses
²Proportioning valve (non-ABS vehicles only)
²Disc brakes
²Drum brakes
²Brake lamp switch
²Brake fluid level switch
²Parking brakes
Front disc brakes control the braking of the front
wheels; rear braking is controlled by rear drum
brakes or rear disc brakes depending on options.
The hydraulic brake system is diagonally split on
both the non-antilock braking systems and antilock
braking systems. That means the left front and right
rear brakes are on one hydraulic circuit and the right
front and left rear are on the other.
For information on the brake lamp switch, (Refer
to 8 - ELECTRICAL/LAMPS/LIGHTING - EXTERI-
OR/BRAKE LAMP SWITCH - DESCRIPTION)Vehicles equipped with the optional antilock brake
system (ABS) use a system designated Mark 20e. It
is available with or without traction control. This
system shares most base brake hardware used on
vehicles without ABS. ABS components are described
in detail in ANTILOCK BRAKE SYSTEM.DESCRIPTION - BASE BRAKES (EXPORT)
Four-Wheel Disc Antilock Brakes are standard on
all models.
OPERATION - BASE BRAKES
When a vehicle needs to be stopped, the driver
applies the brake pedal. The brake pedal pushes the
input rod of the power brake booster into the booster.
The booster uses vacuum to ease pedal effort as force
is transferred through the booster to the master cyl-
inder. The booster's output rod pushes in the master
cylinder's primary and secondary pistons applying
hydraulic pressure through the chassis brake tubes
to the brakes at each tire and wheel assembly.
The parking brakes are foot-operated. When
applied, the parking brake lever pulls on cables that
actuate brake shoes at each rear wheel. These shoes
come in contact with a hub mounted drum (drum for
disc/drum brakes or drum-in-hat for disc/disc brakes)
and hold it in place.
RSBRAKES - BASE5-3
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movement with rubber isolated suspension
crossmember.
(3) Install the four chassis brake tubes into the
outlet ports of the junction block. Tighten all 6 tube
nuts to a torque of 17 N´m (145 in. lbs.).
(4) If the vehicle is equipped with speed control,
perform the following:
(a) Install the speed control servo with its
mounting nuts.
(b) Connect the wiring harness to the speed con-
trol servo.
(c) Install the battery tray (Refer to 8 - ELEC-
TRICAL/BATTERY SYSTEM/TRAY - INSTALLA-
TION).
(d) Install the screw securing the coolant filler
neck to the battery tray.
(e) Reconnect the vacuum hose connector at the
tank built into the battery tray.
(f) Install the battery (Refer to 8 - ELECTRI-
CAL/BATTERY SYSTEM/BATTERY - INSTALLA-
TION).
(g) Install the battery shield.
(5) Remove the brake pedal holder.
(6) Connect negative cable back on negative post of
the battery.
(7) Bleed the brake system thoroughly to ensure
that all air has been expelled from the hydraulic sys-
tem. (Refer to 5 - BRAKES - STANDARD PROCE-
DURE).
(8) Road test the vehicle to verify proper operation
of the brake system.
MASTER CYLINDER
DESCRIPTION
DESCRIPTION
The master cylinder is located on the power brake
booster in the engine compartment on the driver's
side (Fig. 46). This vehicle uses 3 different master
cylinders. Master cylinder usage depends on what
type of brake system the vehicle is equipped with.
CAUTION: Master cylinders are not interchangeable
between systems. Performance and stopping dis-
tance issues will result if the incorrect master cyl-
inder is installed on the vehicle.
For information on master cylinder application,
bore and type, view the following table:
BRAKE SYSTEMMASTER CYLINDER
BORE/TYPE
Disc/Drum - ABS23.8 mm (15/16 in.)
Conventional
Compensating Port
Disc/Drum - Non-ABS23.8 mm (15/16 in.)
Conventional
Compensating Port
Disc/Disc - ABS25.4 mm (1.0 in.)
Conventional
Compensating Port
Disc/Disc ABS With
Traction Control25.4 mm (1.0 in.) Dual
Center Port
Fig. 45 NON-ABS JUNCTION BLOCK
1 - MASTER CYLINDER
2 - JUNCTION BLOCK
3 - SUSPENSION CROSSMEMBER
4 - MOUNTING BOLTS
Fig. 46 Master Cylinder And Booster Location
1 - MASTER CYLINDER
2 - POWER BRAKE BOOSTER
5 - 34 BRAKES - BASERS
JUNCTION BLOCK (Continued)
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CAUTION: When replacing a master cylinder, be
sure to use the correct master cylinder for the type
of brake system the vehicle is equipped with.
The body of the master cylinder is an anodized alu-
minum casting. It has a machined bore to accept the
master cylinder pistons and threaded ports with
seats for the hydraulic brake line connections.
The brake fluid reservoir is mounted on the top of
the master cylinder. It is made of a see-through
polypropylene type plastic for easy fluid level view-
ing. A brake fluid level switch is attached to the
brake fluid reservoir.
The master cylinder is not a repairable component
and must be replaced if diagnosed to be functioning
improperly. The brake fluid reservoir and brake fluid
level switch can be replaced separately.
CAUTION: Do not hone the bore of the cylinder as
this will remove the anodized surface from the bore.
DESCRIPTION - RHD
The master cylinder used on right hand drive
(RHD) vehicles functions similarly to that used on
left hand drive (LHD) vehicles. The RHD master cyl-
inder, as well as the RHD power brake booster, is
located in the same area, but lower in the engine
compartment than LHD models (Fig. 47). For that
reason an extension manifold is placed between the
fluid reservoir and master cylinder housing allowing
the fluid reservoir to be positioned in the same loca-
tion as on LHD models.
OPERATION
When the brake pedal is depressed, the master cyl-
inder primary and secondary pistons apply brake
pressure through the chassis tubes to the brakes at
each tire and wheel assembly.
The master cylinder primary outlet port supplies
hydraulic pressure to the right front and left rear
brakes. The secondary outlet port supplies hydraulic
pressure to the left front and right rear brakes.
STANDARD PROCEDURE - MASTER CYLINDER
BLEEDING
CAUTION: When clamping master cylinder in vise,
only clamp master cylinder by its mounting flange.
Do not clamp master cylinder piston rod, reservoir,
seal or body.
(1) Clamp master cylinder in a vise.
NOTE: Use correct bleeder tubes when bleeding
master cylinder. Master cylinder outlet ports vary in
size and type depending on whether master cylin-
der is for a vehicle equipped with traction control or
not. Traction control equipped master cylinders
require the additional use of ISO style flare adapt-
ers supplied in Special Tool Package 8822 to be
used in conjunction with Bleeder Tubes, Special
Tool Package 8358.
(2) Attach special tools for bleeding master cylin-
der in the following fashion:
(a)For non-traction control equipped mas-
ter cylinders, thread a Bleeder Tube, Special Tool
8358±1, into each outlet port. Tighten each tube to
17 N´m (145 in. lbs.) torque. Flex bleeder tubes and
place open ends into mouth of fluid reservoir as far
down as possible (Fig. 48).
(b)For traction control equipped master
cylinders, thread one Adapter, Special Tool
8822±2, in each outlet port. Tighten Adapters to 17
N´m (145 in. lbs.) torque. Next, thread a Bleeder
Tube, Special Tool 8358±1, into each Adapter.
Tighten each tube to 17 N´m (145 in. lbs.) torque.
Flex bleeder tubes and place open ends into mouth
of fluid reservoir as far down as possible (Fig. 48).
NOTE: Make sure open ends of bleeder tubes stay
below surface of brake fluid once reservoir is filled
to proper level.
(3) Fill brake fluid reservoir with Mopartbrake
fluid or equivalent conforming to DOT 3 (DOT 4 and
DOT 4+ are acceptable) specifications. Make sure
fluid level is above tips of bleeder tubes in reservoir
to ensure no air is ingested during bleeding.
Fig. 47 RHD MASTER CYLINDER AND POWER
BRAKE BOOSTER
1 - POWER BRAKE BOOSTER
2 - BRAKE FLUID LEVEL SWITCH
3 - FLUID RESERVOIR
4 - MASTER CYLINDER
RSBRAKES - BASE5-35
MASTER CYLINDER (Continued)
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Page 183 of 2177
(4) Using a wooden dowel as a pushrod (Fig. 48),
slowly depress master cylinder pistons, then release
pressure, allowing pistons to return to released posi-
tion. Repeat several times until all air bubbles are
expelled. Make sure fluid level stays above tips of
bleeder tubes in reservoir while bleeding.
(5) Remove bleeder tubes from master cylinder
outlet ports, then plug outlet ports and install fill cap
on reservoir.
(6) Remove master cylinder from vise.
(7) Install master cylinder on vehicle. (Refer to 5 -
BRAKES - BASE/HYDRAULIC/MECHANICAL/MAS-
TER CYLINDER - INSTALLATION)
REMOVAL
REMOVAL - LHD
CAUTION: Vacuum in the power brake booster must
be pumped down (removed) before removing mas-
ter cylinder from power brake booster. This is nec-
essary to prevent the power brake booster from
sucking in any contamination as the master cylin-
der is removed. This can be done simply by pump-
ing the brake pedal, with the vehicle's engine not
running, until a firm feeling brake pedal is achieved.
(1) With engine not running, pump brake pedal
until a firm pedal is achieved (4-5 strokes).
(2) Disconnect negative battery terminal.(3) Disconnect positive battery terminal.
(4) Remove battery shield.
(5) Remove nut and clamp securing battery to tray,
remove battery.
(6) Thoroughly clean all surfaces of the brake fluid
reservoir and master cylinder. Use only solvent such
as MopartBrake Parts Cleaner or equivalent.
(7) Remove wiring harness connector from brake
fluid level switch in master cylinder brake fluid res-
ervoir (Fig. 49).
(8) Disconnect primary and secondary brake tubes
from master cylinder housing (Fig. 49). Install seal-
ing plugs in the now open brake tube outlet ports.
CAUTION: Before removing the master cylinder
from the power brake vacuum booster, the master
cylinder and vacuum booster must be thoroughly
cleaned. This must be done to prevent dirt particles
from falling into the power brake vacuum booster.
(9) Clean area where master cylinder assembly
attaches to power brake booster. Use only a solvent
such as MopartBrake Parts Cleaner or equivalent.
(10) Remove two nuts attaching master cylinder to
power brake booster (Fig. 50).
(11) Slide master cylinder straight out of power
brake booster.
CAUTION: A seal on the rear of the master cylinder
is used to create the seal for holding vacuum in the
power brake vacuum booster. The vacuum seal on
the master cylinder MUST be replaced whenever the
master cylinder is removed from the power brake
vacuum booster.
Fig. 48 Master Cylinder Set Up For Bleeding
1 - BLEEDER TUBES 8358
2 - WOODEN DOWEL
3 - ADAPTER 8822-2 (USE ONLY ON TRACTION CONTROL
EQUIPPED MASTER CYLINDERS)
4 - ADAPTER 8822-2 (USE ONLY ON TRACTION CONTROL
EQUIPPED MASTER CYLINDERS)
Fig. 49 MASTER CYLINDER AND BOOSTER
1 - POWER BRAKE BOOSTER
2 - BOOSTER IDENTIFICATION LABEL
3 - FLUID LEVEL SWITCH CONNECTOR
4 - PRIMARY BRAKE TUBE NUT
5 - SECONDARY BRAKE TUBE NUT
6 - MASTER CYLINDER
5 - 36 BRAKES - BASERS
MASTER CYLINDER (Continued)
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BRAKES - ABS
TABLE OF CONTENTS
page page
BRAKES - ABS
DESCRIPTION
DESCRIPTION - ANTILOCK BRAKE
SYSTEM............................75
DESCRIPTION - ANTILOCK BRAKE
SYSTEM (EXPORT)....................75
DESCRIPTION - ELECTRONIC VARIABLE
BRAKE PROPORTIONING...............75
DESCRIPTION - TRACTION CONTROL
SYSTEM............................76
OPERATION
OPERATION - ANTILOCK BRAKE SYSTEM . . 76
OPERATION - ELECTRONIC VARIABLE
BRAKE PROPORTIONING...............77
OPERATION - TRACTION CONTROL
SYSTEM............................77
CAUTION
CAUTIONS..........................78
STANDARD PROCEDURE - ANTILOCK BRAKE
SYSTEM BLEEDING...................78
SPECIFICATIONS
ABS FASTENER TORQUE...............79
TONE WHEEL RUNOUT................79
WHEEL SPEED SENSOR AIR GAP........79
FRONT WHEEL SPEED SENSOR
REMOVAL.............................79
INSTALLATION.........................80
REAR WHEEL SPEED SENSOR - AWD
REMOVAL.............................80INSTALLATION.........................80
REAR WHEEL SPEED SENSOR - FWD
REMOVAL.............................81
INSTALLATION.........................81
TONE WHEEL
INSPECTION - TONE WHEEL..............82
TRACTION CONTROL SWITCH
DIAGNOSIS AND TESTING - TRACTION
CONTROL SWITCH....................82
HYDRAULIC/MECHANICAL
OPERATION - HYDRAULIC CIRCUITS AND
VALVES .............................83
HCU (HYDRAULIC CONTROL UNIT)
DESCRIPTION.........................89
OPERATION...........................89
ICU (INTEGRATED CONTROL UNIT)
DESCRIPTION.........................89
OPERATION...........................90
REMOVAL
REMOVAL - LHD......................90
REMOVAL - RHD......................91
DISASSEMBLY - ICU....................93
ASSEMBLY - ICU.......................94
INSTALLATION
INSTALLATION - LHD..................94
INSTALLATION - RHD..................95
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.
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-
RSBRAKES - ABS5-75
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tioning valve. The EVBP system uses the ABS sys-
tem to control the slip of the rear wheels in partial
braking range. The braking force of the rear wheels
is controlled electronically by using the inlet and out-
let 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 feed-
back.
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 the four wheel circuits is modulated to
prevent any wheel from locking. Each wheel circuit is
designed with a set of electric solenoids to allow mod-ulation, although for vehicle 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 sur-
face 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 - 76 BRAKES - ABSRS
BRAKES - ABS (Continued)
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Page 224 of 2177
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 - ABS5-77
BRAKES - ABS (Continued)
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Page 229 of 2177
NOTE: Make sure wheel speed sensor stays clean
and dry as it is installed into the hub and bearing
cap.
(1) 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.
(2) 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.
(3) Install secondary (yellow) retaining clip over
wheel speed sensor head and engage the tabs on each
side.
(4) Route sensor cable under leaf spring along rear
of axle. Install speed sensor cable into routing clips
on rear brake flex hose (Fig. 3).
(5) 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.).
(6) 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.
(7) Install speed sensor cable grommet into hole in
floor pan making sure grommet is fully seated into
hole.
(8) Lower vehicle.
(9) 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 just
the 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 column shroud.
(2) Disconnect traction control switch harness from
column harness below column.
(3) Using an ohmmeter, check for continuity read-
ing between pins. Refer to TRACTION CONTROL
SWITCH CONTINUITY test table and (Fig. 5).
TRACTION CONTROL SWITCH CONTINUITY
SWITCH POSITION CONTINUITY BETWEEN
ACTUATED PINS 1 AND 2
ILLUMINATION PINS 1 AND 3
Fig. 5 TRACTION CONTROL SWITCH CONNECTOR
5 - 82 BRAKES - ABSRS
REAR WHEEL SPEED SENSOR - FWD (Continued)
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