pump JEEP GRAND CHEROKEE 2003 WJ / 2.G User Guide

(12) Install cover and tighten bolts in a criss-cross
pattern to 41 N´m (30 ft. lbs.).
(13) Refill the differential with Mopar Hypoid
Gear Lubricant or equivalent to bottom of the fill
plug hole.
(14) Install fill hole plug.
(15) Remove support and lower the vehicle.
DIFFERENTIAL - TRAC-LOK
DIAGNOSIS AND TESTING
The most common problem is a chatter noise when
turning corners. Before removing the unit for repair,
drain, flush and refill the axle with the specified
lubricant. A container of Mopar Trac-loktLubricant
(friction modifier) should be added after repair ser-
vice or during a lubricant change.
After changing the lubricant, drive the vehicle and
make 10 to 12 slow, figure-eight turns. This maneu-
ver will pump lubricant through the clutches. This
will correct the condition in most instances. If the
chatter persists, clutch damage could have occurred.
DIFFERENTIAL TEST
The differential can be tested without removing the
differential case by measuring rotating torque. Make
sure brakes are not dragging during this measure-
ment.
(1) Place blocks in front and rear of both front
wheels.
(2) Raise one rear wheel until it is completely off
the ground.
(3) Engine off, transmission in neutral, and park-
ing brake off.
(4) Remove wheel and bolt Special Tool 6790 or
equivalent tool to studs.
(5) Use torque wrench on special tool to rotate
wheel and read rotating torque (Fig. 56).
(6) If rotating torque is less than 41 N´m (56 ft.
lbs.) or more than 271 N´m (200 ft. lbs.) on either
wheel the unit should be serviced.
DISASSEMBLY
(1) Clamp side gear Holding Fixture 6965 in a vise
and position the differential case on the Holding Fix-
ture (Fig. 57).
(2) Remove ring gear if the ring gear is to be
replaced. The Trac-loktdifferential can be serviced
with the ring gear installed.
Fig. 56 ROTATING TORQUE TEST
1 - SPECIAL TOOL WITH BOLT IN CENTER HOLE
2 - TORQUE WRENCH
Fig. 57 DIFFERENTIAL CASE FIXTURE
1 - HOLDING FIXTURE
2 - VISE
3 - DIFFERENTIAL
WJREAR AXLE - 226RBA 3 - 119
DIFFERENTIAL (Continued)

(2) If complaint was based on noise when braking,
check suspension components. Jounce front and rear
of vehicle and listen for noise that might be caused
by loose, worn or damaged suspension or steering
components.
(3) Inspect brake fluid level and condition. Note
that the brake reservoir fluid level will decrease in
proportion to normal lining wear.Also note that
brake fluid tends to darken over time. This is
normal and should not be mistaken for contam-
ination.
(a) If fluid level is abnormally low, look for evi-
dence of leaks at calipers, brake lines, master cyl-
inder, and HCU.
(b) If fluid appears contaminated, drain out a
sample to examine. System will have to be flushed
if fluid is separated into layers, or contains a sub-
stance other than brake fluid. The system seals,
cups, hoses, master cylinder, and HCU will also
have to be replaced after flushing. Use clean brake
fluid to flush the system.
(4) Check parking brake operation. Verify free
movement and full release of cables and lever. Also
note if vehicle was being operated with parking
brake partially applied.
(5) Check brake pedal operation. Verify that pedal
does not bind and has adequate free play. If pedal
lacks free play, check pedal and power booster for
being loose or for bind condition. Do not road test
until condition is corrected.
(6) Check booster vacuum check valve and hose.
(7) If components checked appear OK, road test
the vehicle.
ROAD TESTING
(1) If complaint involved low brake pedal, pump
pedal and note if it comes back up to normal height.
(2) Check brake pedal response with transmission
in neutral and engine running. Pedal should remain
firm under constant foot pressure.
(3) During road test, make normal and firm brake
stops in 25-40 mph range. Note faulty brake opera-
tion such as low pedal, hard pedal, fade, pedal pulsa-
tion, pull, grab, drag, noise, etc.
(4) Attempt to stop the vehicle with the parking
brake only (do not exceed 25 mph) and note grab,
drag, noise, etc.
PEDAL FALLS AWAY
A brake pedal that falls away under steady foot
pressure is generally the result of a system leak. The
leak point could be at a brake line, fitting, hose, or
caliper. If leakage is severe, fluid will be evident at
or around the leaking component.Internal leakage (seal by-pass) in the master cylin-
der caused by worn or damaged piston cups, may
also be the problem cause.
An internal leak in the ABS system may also be
the problem with no visual fluid leak.
LOW PEDAL
If a low pedal is experienced, pump the pedal sev-
eral times. If the pedal comes back up, the most
likely causes are worn linings, rotors, or calipers are
not sliding on the slide pins. The proper course of
action is to inspect and replace all worn component.
SPONGY PEDAL
A spongy pedal is most often caused by air in the
system. However substandard brake hoses can cause
a spongy pedal. The proper course of action is to
bleed the system, and replace substandard quality
brake hoses if suspected.
HARD PEDAL OR HIGH PEDAL EFFORT
A hard pedal or high pedal effort may be due to
lining that is water soaked, contaminated, glazed, or
badly worn. The power booster, check valve, check
valve seal/grommet or vacuum leak could also cause
a hard pedal or high pedal effort.
PEDAL PULSATION
Pedal pulsation is caused by components that are
loose, or beyond tolerance limits.
The primary cause of pulsation are disc brake
rotors with excessive lateral runout or thickness vari-
ation. Other causes are loose wheel bearings or cali-
pers and worn, damaged tires.
NOTE: Some pedal pulsation may be felt during
ABS activation.
BRAKE DRAG
Brake drag occurs when the lining is in constant
contact with the rotor or drum. Drag can occur at one
wheel, all wheels, fronts only, or rears only.
Drag is a product of incomplete brake release.
Drag can be minor or severe enough to overheat the
linings, rotors and park brake drums.
Minor drag will usually cause slight surface charring
of the lining. It can also generate hard spots in rotors
and park brake drums from the overheat-cool down pro-
cess. In most cases, the rotors, wheels and tires are
quite warm to the touch after the vehicle is stopped.
Severe drag can char the brake lining all the way
through. It can also distort and score rotors to the
point of replacement. The wheels, tires and brake
components will be extremely hot. In severe cases,
the lining may generate smoke as it chars from over-
heating.
WJBRAKES - BASE 5 - 3
BRAKES - BASE (Continued)

NOTE: The front outer brake shoes are equipped
with a wear indicator. The indicator will produce an
audible noise when it contacts the rotor surface.
BRAKE CHATTER
Brake chatter is usually caused by loose or worn
components, or glazed/burnt lining. Rotors with hard
spots can also contribute to chatter. Additional causes
of chatter are out-of-tolerance rotors, brake lining not
securely attached to the shoes, loose wheel bearings
and contaminated brake lining.
THUMP/CLUNK NOISE
Thumping or clunk noises during braking are fre-
quentlynotcaused by brake components. In many
cases, such noises are caused by loose or damaged
steering, suspension, or engine components.
STANDARD PROCEDURE
STANDARD PROCEDURE - MANUAL BLEEDING
Use Mopar brake fluid, or an equivalent quality
fluid meeting SAE J1703-F and DOT 3 standards
only. Use fresh, clean fluid from a sealed container at
all times.
Do not pump the brake pedal at any time while
bleeding. Air in the system will be compressed into
small bubbles that are distributed throughout the
hydraulic system. This will make additional bleeding
operations necessary.
Do not allow the master cylinder to run out of fluid
during bleed operations. An empty cylinder will allow
additional air to be drawn into the system. Check the
cylinder fluid level frequently and add fluid as
needed.
Bleed only one brake component at a time in the
following sequence:
(1) Fill the master cylinder reservoir with brake
fluid.
(2) If calipers are overhauled, open all caliper
bleed screws. Then close each bleed screw as fluid
starts to drip from it. Top off master cylinder reser-
voir once more before proceeding.
(3) Attach one end of bleed hose to bleed screw
and insert opposite end in glass container partially
filled with brake fluid (Fig. 1). Be sure end of bleed
hose is immersed in fluid.
(4) Open up bleeder, then have a helper press
down the brake pedal. Once the pedal is down close
the bleeder. Repeat bleeding until fluid stream is
clear and free of bubbles. Then move to the next
wheel.
STANDARD PROCEDURE - PRESSURE
BLEEDING
Use Mopar brake fluid, or an equivalent quality
fluid meeting SAE J1703-F and DOT 3 standards
only. Use fresh, clean fluid from a sealed container at
all times.
Do not pump the brake pedal at any time while
bleeding. Air in the system will be compressed into
small bubbles that are distributed throughout the
hydraulic system. This will make additional bleeding
operations necessary.
Do not allow the master cylinder to run out of fluid
during bleed operations. An empty cylinder will allow
additional air to be drawn into the system. Check the
cylinder fluid level frequently and add fluid as
needed.
Bleed only one brake component at a time in the
following sequence:
Follow the manufacturers instructions carefully
when using pressure equipment. Do not exceed the
tank manufacturers pressure recommendations. Gen-
erally, a tank pressure of 51-67 kPa (15-20 psi) is suf-
ficient for bleeding.
Fill the bleeder tank with recommended fluid and
purge air from the tank lines before bleeding.
Do not pressure bleed without a proper master cyl-
inder adapter. The wrong adapter can lead to leak-
age, or drawing air back into the system. Use
adapter provided with the equipment or Adapter
6921.
Fig. 1 Bleed Hose Setup
1 - BLEED HOSE
2 - FLUID CONTAINER PARTIALLY FILLED WITH FLUID
WJBRAKES - BASE 5 - 5
BRAKES - BASE (Continued)

(8) Install wheel and tire assembly.
(9) Remove support and lower vehicle.
(10) Pump brake pedal until caliper pistons and
brake shoes are seated and a firm brake pedal is
obtained.
(11) Fill brake fluid.
INSTALLATION - REAR DISC BRAKE SHOES
(1) Install the inboard brake shoe onto the caliper
(Fig. 17).
(2) Install the outboard brake shoe onto the caliper
anchor (Fig. 18).
(3) Lubricate the slide pins and slide pin bushings
with Dow Corningtgrease G807 or the grease pro-
vided with the brake shoes.
(4) Install caliper on the anchor.
(5) Install the caliper slide pin and tighten to
29-41 N´m (21-30 ft. lbs.).
(6) Install the caliper slide pin bushing caps.
(7) Install the caliper support spring in the top
end of the caliper and under the anchor. Then installother end into the lower caliper hole. Hold the spring
into the caliper hole with your thumb while prying
the end of the spring out and down under the anchor
with a screw drive.
(8) Install wheel and tire assembly.
(9) Remove support and lower vehicle.
(10) Pump brake pedal until caliper piston and
brake shoes are seated and a firm brake pedal is
obtained.
(11) Fill brake fluid level if necessary.
DISC BRAKE CALIPERS
REMOVAL
REMOVAL - FRONT DISC BRAKE CALIPER
(1) Raise and support vehicle.
(2) Remove front wheel and tire assembly.
(3) Drain small amount of fluid from master cylin-
der brake reservoir withcleansuction gun.
(4) Bottom caliper pistons into the caliper by pry-
ing the caliper over (Fig. 19).
Fig. 18 Outboard Brake Shoe
1 - OUTBOARD BRAKE SHOE
2 - CALIPER ANCHOR
3 - ROTOR
Fig. 19 Bottoming Caliper Piston
1 - ROTOR
2 - CALIPER
5 - 14 BRAKES - BASEWJ
BRAKE PADS / SHOES (Continued)

OPERATION
The master cylinder bore contains a primary and
secondary piston. The primary piston supplies
hydraulic pressure to the front brakes. The secondary
piston supplies hydraulic pressure to the rear brakes.
The master cylinder reservoir stores reserve brake
fluid for the hydraulic brake circuits.
DIAGNOSIS AND TESTING - MASTER
CYLINDER/POWER BOOSTER
NOTE: Inspect and repair any external fluid leaks
before performing test.
(1) Start engine and check booster vacuum hose
connections. A hissing noise indicates vacuum leak.
Correct any vacuum leak before proceeding.
(2)
Stop engine and shift transmission into Neutral.
(3) Pump brake pedal until all vacuum reserve in
booster is depleted.
(4) Press and hold brake pedal under light foot
pressure. The pedal should hold firm, if the pedal
falls away the master cylinder or HCU may be faulty
(internal leakage).
(5) Start engine and note pedal action. It should
fall away slightly under light foot pressure then hold
firm. If no pedal action is discernible, power booster,
vacuum supply, or vacuum check valve is faulty. Pro-
ceed to the POWER BOOSTER VACUUM TEST.
(6) If the POWER BOOSTER VACUUM TEST
passes, rebuild booster vacuum reserve as follows:
Release brake pedal. Increase engine speed to 1500
rpm, close the throttle and turn off the engine.
(7) Wait a minimum of 90 seconds and try brake
action again. Booster should provide two or more vac-
uum assisted pedal applications. If vacuum assist is
not provided, some component of the booster is faulty.
POWER BOOSTER VACUUM TEST
(1) Connect vacuum gauge to booster check valve
with short length of hose and T-fitting (Fig. 48).
(2) Start and run engine at curb idle speed for one
minute.
(3) Observe the vacuum supply. If vacuum supply
is not adequate, repair vacuum supply.
(4) Clamp hose shut between vacuum source and
check valve.
(5) Stop engine and observe vacuum gauge.
(6) If vacuum drops more than one inch HG (33
millibars) within 15 seconds, booster diaphragm,
check valve or check valve seal/grommet is faulty.
POWER BOOSTER CHECK VALVE TEST
(1) Disconnect vacuum hose from check valve.
(2)
Remove check valve and valve seal from booster.
(3) Use a hand operated vacuum pump for test.(4) Apply 51-67 kPa (15-20 in.) vacuum at large
end of check valve (Fig. 49).
(5) Vacuum should hold steady. If gauge on pump
indicates vacuum loss the check valve and seal
should be replaced.
Fig. 48 Typical Booster Vacuum Test Connections
1 - TEE FITTING
2 - SHORT CONNECTING HOSE
3 - CHECK VALVE
4 - CHECK VALVE HOSE
5 - CLAMP TOOL
6 - INTAKE MANIFOLD
7 - VACUUM GAUGE
Fig. 49 Vacuum Check Valve And Seal
1 - BOOSTER CHECK VALVE
2 - APPLY TEST VACUUM HERE
3 - VALVE SEAL
5 - 24 BRAKES - BASEWJ
MASTER CYLINDER (Continued)

INSTALLATION
INSTALLATION - FRONT DISC BRAKE ROTOR
NOTE: If a new rotor is installed it must be match
mounted to the hub/bearing.
(1) Install rotor on hub studs in its original loca-
tion.
(2) Install the caliper anchor assembly on the
knuckle. Install anchor bolts and tighten to 90-115
N´m (66-85 ft. lbs.).
(3) Install wheel and tire assembly.
(4) Remove support and lower the vehicle.
(5) Pump brake pedal to seat caliper pistons and
brake shoes. Do not move vehicle until firm brake
pedal is obtained.
INSTALLATION - REAR DISC BRAKE ROTOR
(1) Install rotor on axle studs.
(2) Install the caliper anchor assembly.
(3) Install anchor bolts and tighten to 90-115 N´m
(66-85 ft. lbs.).
(4) Install wheel and tire assembly.
(5) Remove support and lower the vehicle.
(6) Pump brake pedal until caliper pistons and
brake shoes are seated.
PARKING BRAKE
OPERATION
The parking brakes operated by a automatic ten-
sioner mechanism built into the hand lever and cable
system. The front cable is connected to the hand
lever and the equalizer. The rear cables attached to
the equalizer and the parking brake shoe actuator.
A set of drum type brake shoes are used for park-
ing brakes. The shoes are mounted to the rear disc
brake adaptor. The parking brake drum is integrated
into the rear disc brake rotor.
Parking brake cable adjustment is controlled by an
automatic tensioner mechanism. The only adjust-
ment if necessary is to the park brake shoes if the
linings are worn.
DIAGNOSIS AND TESTING - PARKING BRAKE
NOTE: Parking brake adjustment is controlled by an
automatic cable tensioner and does not require
adjustment. The only adjustment that may be nec-
essary would be to the park brake shoes if they are
worn.
The parking brake switch is in circuit with the red
warning lamp in the dash. The switch will cause the
lamp to illuminate only when the parking brakes are
applied. If the lamp remains on after parking brake
release, the switch or wires are faulty.
If the red lamp comes on a fault has occurred in
the front or rear brake hydraulic system.
If the red warning lamp and yellow warning lamp
come on, the electronic brake distribution may be at
fault.
In most cases, the actual cause of an improperly
functioning parking brake (too loose/too tight/won't
hold), can be traced to a parking brake component.
NOTE: The leading cause of improper parking brake
operation, is excessive clearance between the park-
ing brake shoes and the shoe braking surface.
Excessive clearance is a result of lining and/or
drum wear, drum surface machined oversize.
Excessive parking brake lever travel (sometimes
described as a loose lever or too loose condition), is
the result of worn brake shoes, improper brake shoe
adjustment, or improperly assembled brake parts.
A too loose condition can also be caused by inoper-
ative or improperly assembled parking brake shoe
parts.
A condition where the parking brakes do not hold,
will most probably be due to a wheel brake compo-
nent.
Items to look for when diagnosing a parking brake
problem, are:
²Brake shoe wear
²Drum surface (in rear rotor) machined oversize
²Front cable not secured to lever
²Rear cable not attached to actuator
²Rear cable seized
²Parking brake lever not seated
²Parking brake lever bind
5 - 34 BRAKES - BASEWJ
ROTORS (Continued)

BRAKES - ABS
TABLE OF CONTENTS
page page
BRAKES - ABS
DESCRIPTION.........................41
OPERATION...........................41
DIAGNOSIS AND TESTING - ANTILOCK
BRAKES............................42
STANDARD PROCEDURE - BLEEDING ABS
BRAKE SYSTEM......................42
SPECIFICATIONS
TORQUE CHART......................42
ELECTRIC BRAKE
DESCRIPTION.........................43
OPERATION...........................43
FRONT WHEEL SPEED SENSOR
DESCRIPTION.........................43
OPERATION...........................43
REMOVAL.............................43INSTALLATION.........................43
G-SWITCH
DESCRIPTION.........................44
OPERATION...........................44
REMOVAL.............................44
INSTALLATION.........................44
REAR WHEEL SPEED SENSOR
DESCRIPTION.........................45
OPERATION...........................45
REMOVAL.............................45
INSTALLATION.........................46
HCU (HYDRAULIC CONTROL UNIT)
DESCRIPTION.........................46
OPERATION...........................46
REMOVAL.............................47
INSTALLATION.........................47
BRAKES - ABS
DESCRIPTION
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 hydraulic system is a three channel design.
The front brakes are controlled individually and the
rear brakes in tandem.
The ABS electrical system is separate from other
vehicle electrical circuits. A separate controller oper-
ates the system.
OPERATION
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.
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 check occurs after the ignition switch is
turned to Run position. The dynamic check occurs
when vehicle road speed reaches approximately 30kph (18 mph). During the dynamic check, the CAB
briefly cycles the pump and solenoids to verify oper-
ation.
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.
ANTILOCK BRAKING
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. A sensor at each wheel converts 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.
WJBRAKES - ABS 5 - 41

DIAGNOSIS AND TESTING - ANTILOCK
BRAKES
The ABS brake system performs several self-tests
every time the ignition switch is turned on and the
vehicle is driven. The CAB monitors the systems
input and output circuits to verify the system is oper-
ating correctly. If the on board diagnostic system
senses that a circuit is malfunctioning the system
will set a trouble code in its memory.
NOTE: An audible noise may be heard during the
self-test. This noise should be considered normal.
NOTE: The MDS or DRB III scan tool is used to
diagnose the ABS system. For additional informa-
tion refer to the Electrical section. For test proce-
dures refer to the Chassis Diagnostic Manual.
STANDARD PROCEDURE - BLEEDING ABS
BRAKE SYSTEM
ABS system bleeding requires conventional bleed-
ing methods plus use of the DRB scan tool. The pro-cedure involves performing a base brake bleeding,
followed by use of the scan tool to cycle and bleed the
HCU pump and solenoids. A second base brake bleed-
ing procedure is then required to remove any air
remaining in the system.
(1) Perform base brake bleeding. (Refer to 5 -
BRAKES - STANDARD PROCEDURE) OR (Refer to
5 - BRAKES - STANDARD PROCEDURE).
(2) Connect scan tool to the Data Link Connector.
(3) Select ANTILOCK BRAKES, followed by MIS-
CELLANEOUS, then ABS BRAKES. Follow the
instructions displayed. When scan tool displays TEST
COMPLETE, disconnect scan tool and proceed.
(4) Perform base brake bleeding a second time.
(Refer to 5 - BRAKES - STANDARD PROCEDURE)
OR (Refer to 5 - BRAKES - STANDARD PROCE-
DURE).
(5) Top off master cylinder fluid level and verify
proper brake operation before moving vehicle.
SPECIFICATIONS
TORQUE CHART
TORQUE SPECIFICATIONS
DESCRIPTION N´m Ft. Lbs. In. Lbs.
G-Sensor Bolt 5.6 Ð 50
Hydraulic Control Unit/Controller
Antilock Brakes
Mounting Bolts12 9 125
Hydraulic Control Unit/Controller
Antilock Brakes
Brake Lines16 Ð 144
Hydraulic Control Unit/Controller
Antilock Brakes
CAB Screws1.8 Ð 16
Wheel Speed Sensors
Front Sensor Bolt12-14 106-124 Ð
Wheel Speed Sensors
Rear Sensor Bolt12-14 106-124 Ð
5 - 42 BRAKES - ABSWJ
BRAKES - ABS (Continued)

INSTALLATION
(1) Insert the sensor through the backing plate
(Fig. 9).
(2) Apply Mopar Lock N' Seal or Loctite 242tto
the original sensor bolt. Use a new bolt if the original
is worn or damaged.
(3) Tighten the sensor bolt to 12-14 N´m (106-124
in. lbs.).
(4) Secure the sensor wire in the brackets and the
retainers on the rear brake lines. Verify that the sen-
sor wire is secure and clear of the rotating compo-
nents.
(5) Route the sensor wires to the rear seat area.
(6) Feed the sensor wires the through floorpan
access hole and seat the sensor grommets into the
floorpan.
(7) Remove the support and lower the vehicle.(8) Fold the rear seat and carpet forward for
access to the sensor wires and connectors.
(9) Connect the sensor wires to the harness con-
nectors.
(10) Reposition the carpet and fold the rear seat
down.
HCU (HYDRAULIC CONTROL
UNIT)
DESCRIPTION
The HCU consists of a valve body, pump motor,
and wire harness.
OPERATION
Accumulators in the valve body store extra fluid
released to the system for ABS mode operation. The
pump is used to clear the accumulator of brake fluid
and is operated by a DC type motor. The motor is
controlled by the CAB.
The valves modulate brake pressure during
antilock braking 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 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.
During antilock braking, solenoid valve pressure
modulation occurs in three stages, pressure increase,
pressure hold, and pressure decrease. The valves are
all contained in the valve body portion of the HCU.
PRESSURE DECREASE
The outlet valve is opened and the inlet valve is
closed 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
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.
Fig. 8 Sensor Mounting Bolt
1 - WHEEL SPEED SENSOR
2 - MOUNTING BOLT
Fig. 9 Wheel Speed Sensor
1 - WHEEL SPEED SENSOR
2 - BACKING PLATE
5 - 46 BRAKES - ABSWJ
REAR WHEEL SPEED SENSOR (Continued)

COOLING
TABLE OF CONTENTS
page page
COOLING
DESCRIPTION
DESCRIPTION - COOLING SYSTEM 4.7L
ENGINE..............................1
DESCRIPTION - COOLING SYSTEM
ROUTING 4.7L ENGINE..................1
DESCRIPTIONÐCOOLING SYSTEM 4.0L
ENGINE..............................1
DESCRIPTIONÐCOOLING SYSTEM
ROUTING 4.0L ENGINE..................1
DESCRIPTIONÐHOSE CLAMPS...........1
OPERATION
OPERATIONÐCOOLING SYSTEM.........2
OPERATIONÐHOSE CLAMPS............2
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTINGÐON-BOARD
DIAGNOSTICS (OBD)...................3
DIAGNOSIS AND TESTINGÐPRELIMINARY
CHECKS.............................3
DIAGNOSIS AND TESTING - COOLING
SYSTEM DIAGNOSIS CHART.............5
DIAGNOSIS AND TESTING - COOLING
SYSTEM LEAKS......................10DIAGNOSIS AND TESTING - COOLING
SYSTEM DEAERATION.................12
STANDARD PROCEDURE
STANDARD PROCEDUREÐDRAINING
COOLING SYSTEM 4.7L ENGINE.........12
STANDARD PROCEDURE - REFILLING
COOLING SYSTEM 4.7L ENGINE.........12
STANDARD PROCEDURE - DRAINING
COOLING SYSTEM - 4.0L ENGINE........13
STANDARD PROCEDURE - REFILLING
COOLING SYSTEM - 4.0L ENGINE........13
STANDARD PROCEDURE - ADDING
ADDITIONAL COOLANT.................13
STANDARD PROCEDURE - COOLING
SYSTEM - REVERSE FLUSHING..........14
SPECIFICATIONS
TORQUE............................14
SPECIAL TOOLS
COOLING...........................15
ACCESSORY DRIVE......................16
ENGINE...............................24
TRANSMISSION.........................55
COOLING
DESCRIPTION
DESCRIPTION - COOLING SYSTEM 4.7L
ENGINE
The cooling system consists of the following items:
²Hydraulic cooling fan and fan drive assembly
²Radiator
²Power steering oil cooler
²Radiator pressure cap
²Thermostat
²Coolant reserve/overflow system
²Transmission oil cooler (if equipped with an
automatic transmission)
²Coolant
²Water pump
²Hoses and hose clamps
DESCRIPTION - COOLING SYSTEM ROUTING
4.7L ENGINE
For cooling system routing refer to (Fig. 1).
DESCRIPTIONÐCOOLING SYSTEM 4.0L
ENGINE
The cooling system consists of:
²A radiator
²Mechanical Cooling Fan
²Thermal viscous fan drive-Low disengaged
²Fan shroud (Fig. 2)
²Radiator pressure cap
²Thermostat
²Coolant reserve/overflow system
²Transmission oil cooler (if equipped with an
automatic transmission)
²Coolant
²Water pump
²Hoses and hose clamps
²Accessory drive belt
DESCRIPTIONÐCOOLING SYSTEM ROUTING
4.0L ENGINE
For cooling system routing refer to (Fig. 3).
DESCRIPTIONÐHOSE CLAMPS
The cooling system utilizes both worm drive and
spring type hose clamps. If a spring type clamp
WJCOOLING 7 - 1