2003 JEEP GRAND CHEROKEE Brake pedal

(5) Install the cluster bezel (Refer to 23 - BODY/
INSTRUMENT PANEL/CLUSTER BEZEL -
INSTALLATION).
(6) Reconnect the negative battery cable.
POWER BRAKE BOOSTER
DESCRIPTION
The booster assembly consists of a housing divided
into separate chambers by two internal diaphragms.
The outer edge of each diaphragm is attached to the
booster housing.
Two push rods are used in the booster. The pri-
mary push rod connects the booster to the brake
pedal. The secondary push rod connects the booster
to the master cylinder to stroke the cylinder pistons.
OPERATION
The atmospheric inlet valve is opened and closed
by the primary push rod. Booster vacuum supply is
through a hose attached to an intake manifold fittingat one end and to the booster check valve at the
other. The vacuum check valve in the booster housing
is a one-way device that prevents vacuum leak back.
Power assist is generated by utilizing the pressure
differential between normal atmospheric pressure
and a vacuum. The vacuum needed for booster oper-
ation is taken directly from the engine intake mani-
fold. The entry point for atmospheric pressure is
through a filter and inlet valve at the rear of the
housing (Fig. 59) .
The chamber areas forward of the booster dia-
phragms are exposed to vacuum from the intake
manifold. The chamber areas to the rear of the dia-
phragms, are exposed to normal atmospheric pres-
sure of 101.3 kilopascals (14.7 pounds/square in.).
Brake pedal application causes the primary push
rod to open the atmospheric inlet valve. This exposes
the area behind the diaphragms to atmospheric pres-
sure. The resulting pressure differential provides the
extra apply force for power assist.
The booster check valve, check valve grommet and
booster seals are serviceable.
WJBRAKES - BASE 5 - 29
PEDAL MOTOR (Continued)

Fig. 59 Power Brake Booster±Typical
1 - VACUUM CHECK VALVE
2 - FRONT DIAPHRAGM
3 - REAR DIAPHRAGM
4 - HOUSING
5 - SEAL
6 - AIR FILTER
7 - PRIMARY PUSH ROD (TO BRAKE PEDAL)8 - ATMOSPHERIC INLET VALVE ASSEMBLY
9 - BOOSTER MOUNTING STUDS (4)
10 - SECONDARY PUSH ROD (TO MASTER CYLINDER)
11 - MASTER CYLINDER MOUNTING STUD (2)
12 - SPRING
5 - 30 BRAKES - BASEWJ
POWER BRAKE BOOSTER (Continued)

REMOVAL
(1) Remove the master cylinder.
(2) Disconnect vacuum hose at booster check valve.
(3) Remove retainer clip (Fig. 60) that holds
booster push rod on pedal pin. Then slide push rod
off pin.
(4) Remove four nuts (Fig. 61) that attach booster
to dash panel.
(5) In engine compartment, slide booster forward,
tilt it upward slightly, and remove it from engine
compartment.
INSTALLATION
(1) Check condition of grommet that secures check
valve in booster. Replace grommet if cut, torn, or
loose.
(2) Install new booster dash seal.
(3) Align and position booster on engine compart-
ment side of dash panel.
(4) Inside passenger compartment:
(a) Lubricate pedal pin Mopar multi-mileage
grease.
(b) Install booster attaching nuts on studs.
Tighten attaching nuts to 39 N´m (29 ft. lbs.).
(c) Slide booster push rod on pedal pin. Then
secure rod to pin with retainer clip.
(5) In engine compartment, attach vacuum hose to
booster check valve.(6) Install the master cylinder with new gasket
and nuts.
CAUTION: The master cylinder installation proce-
dure must be perform as written or damage to the
booster/master cylinder may occur.
(7) Fill and bleed brake system.
ROTORS
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - FRONT DISC
BRAKE ROTOR
ROTOR MINIMUM THICKNESS
Rotor minimum usable thickness is 24.5 mm (0.964
in.). Do not resurface a rotor if machining would
cause thickness to fall below this limit.
Measure rotor thickness at the center of the brake
shoe contact surface. Replace the rotor if worn below
minimum thickness, or if refinishing would reduce
thickness below the allowable minimum.
FRONT ROTOR THICKNESS VARIATION
Variations in rotor thickness will cause pedal pul-
sation, noise and shudder.
Fig. 60 Retainer Clip
1 - RETAINER CLIP
2 - PUSH ROD
3 - PEDAL PIN
Fig. 61 Power Brake Booster Mounting
1 - BOOSTER
2 - DASH PANEL
WJBRAKES - BASE 5 - 31
POWER BRAKE BOOSTER (Continued)

Measure rotor thickness a minimum of six points
around the rotor face. Position the micrometer approx-
imately 19 mm (3/4 in.) from the rotor outer circumfer-
ence for each measurement (Fig. 62).
Thickness should not vary by more than 0.0127 mm
(0.0005 in.) from point to point on the rotor. Refinish or
replace the rotor if necessary.
NOTE: A hub mounted on-vehicle lathe is recom-
mended. This type of lathe trues the rotor to the vehi-
cles hub/bearing.
CAUTION: For vehicles equipped with the Quadra-
Drive System, consisting of the NV-247 transfer case
and a Vari-Lok differential in the front and rear axles,
the following steps must be done prior to the use of a
hub mounted on-vehicle brake lathe. Disconnect the
driveshaft (Refer to 3 - DIFFERENTIAL & DRIVELINE/
PROPELLER SHAFT/PROPELLER SHAFT - REMOVAL)
from the respective axle on which the brake rotors are
being machined. Temporarily remove both brake cali-
pers (Refer to 5 - BRAKES/HYDRAULIC/MECHANICAL/
DISC BRAKE CALIPERS - REMOVAL) from the axle
while disc rotor machining is in process. Both steps
will prevent unnecessary loads to the hub mounted
on-vehicle lathe and speed machining times. Install a
thread lock material to the driveshaft attaching bolts
when reinstalling (Refer to 3 - DIFFERENTIAL & DRIV-
ELINE/PROPELLER SHAFT/PROPELLER SHAFT -
INSTALLATION).
Front rotors and hub/bearings are matched mounted
for minimum lateral runout. Before removing the rotor,
mark the rotor and hub/bearing to maintain original
orientation.
FRONT ROTOR LATERAL RUNOUT
Check rotor lateral runout whenever pedal pulsation,
or rapid, uneven brake lining wear has occurred.
The rotor must be securely clamped to the hub to
ensure an accurate runout measurement. Secure therotor with a minimum of 3 lug nuts and large diameter
flat washers on each stud.
Use a dial indicator to check lateral runout (Fig. 63).
Maximum allowable rotor lateral runout is 0.05 mm
(0.002 in.).
DIAGNOSIS AND TESTING - REAR DISC
BRAKE ROTOR
ROTOR MINIMUM THICKNESS
Minimum usable thickness of the rear disc brake
rotor is 8.5 mm (0.335 in.). The thickness specification
is located on the center section of the rotor.
Never resurface a rotor if machining would cause
thickness to fall below this limit.
Measure rotor thickness at the center of the brake
shoe contact surface. Replace the rotor if worn below
minimum thickness, or if refinishing would reduce
thickness below the allowable minimum.
REAR ROTOR THICKNESS VARIATION
Variations in rotor thickness will cause pedal pulsa-
tion, noise and shudder.
Measure rotor thickness at a minimum of six points
around the rotor face. Position the micrometer approxi-
mately 19 mm (3/4 in.) from the rotor outer circumfer-
ence for each measurement (Fig. 62).
Thickness should not vary by more than 0.0127 mm
(0.0005 in.) from point to point on the rotor. Refinish or
replace the rotor if necessary.
REAR ROTOR LATERAL RUNOUT
Check rotor lateral runout whenever diagnosis indi-
cates pedal pulsation and rapid, uneven brake lining
wear.
The rotor must be securely clamped to the hub to
ensure an accurate runout measurement. Secure the
rotor with the wheel nuts and 4 or 5 large diameter flat
washers on each stud.
Use a dial indicator to check lateral runout (Fig. 63).
Maximum allowable lateral runout is 0.76 mm (0.003 in.).
Fig. 62 Measuring Rotor Thickness Variation
1 - MICROMETER
2 - ROTOR
Fig. 63 Checking Rotor Lateral Runout
1 - DIAL INDICATOR
5 - 32 BRAKES - BASEWJ
ROTORS (Continued)
2002 WJ Service Manual
Publication No. 81-370-02064
02WJ5-32 June, 2002

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

ELECTRONIC CONTROL MODULES
TABLE OF CONTENTS
page page
ELECTRONIC CONTROL MODULES
STANDARD PROCEDURE - PCM/SKIM
PROGRAMMING.......................1
ADJUSTABLE PEDALS MODULE
REMOVAL.............................2
INSTALLATION..........................3
BODY CONTROL MODULE
DESCRIPTION..........................3
OPERATION............................3
DIAGNOSIS AND TESTING - BODY CONTROL
MODULE.............................4
REMOVAL.............................5
INSTALLATION..........................5
COMMUNICATION
DESCRIPTION..........................6
OPERATION............................6
CONTROLLER ANTILOCK BRAKE
DESCRIPTION..........................6
OPERATION............................6
REMOVAL.............................7
INSTALLATION..........................7
DATA LINK CONNECTOR
DESCRIPTION - DATA LINK CONNECTOR.....7
OPERATION - DATA LINK CONNECTOR......7
DOOR MODULE
DESCRIPTION..........................7
OPERATION............................9
DIAGNOSIS AND TESTING - DOOR MODULE . 10
REMOVAL.............................10
INSTALLATION.........................10
MEMORY HEATED SEAT/MIRROR MODULE
DESCRIPTION.........................10OPERATION...........................11
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - HEATED SEAT
MODULE............................11
REMOVAL.............................11
INSTALLATION.........................12
POWERTRAIN CONTROL MODULE
DESCRIPTION
DESCRIPTION - PCM..................12
MODES OF OPERATION................12
DESCRIPTION - 5 VOLT SUPPLIES.......14
DESCRIPTION - IGNITION CIRCUIT SENSE . 14
DESCRIPTION - POWER GROUNDS......15
DESCRIPTION - SENSOR RETURN.......15
OPERATION
OPERATION - PCM....................15
OPERATION - 5 VOLT SUPPLIES.........16
OPERATION - IGNITION CIRCUIT SENSE . . . 16
REMOVAL.............................16
INSTALLATION.........................17
SENTRY KEY IMMOBILIZER MODULE
DESCRIPTION.........................17
OPERATION...........................17
REMOVAL.............................18
INSTALLATION.........................19
TRANSMISSION CONTROL MODULE
DESCRIPTION.........................19
OPERATION...........................19
STANDARD PROCEDURE
STANDARD PROCEDURE - TCM QUICK
LEARN..............................22
ELECTRONIC CONTROL
MODULES
STANDARD PROCEDURE - PCM/SKIM
PROGRAMMING
NOTE: Before replacing the PCM, be sure to check
the related component/circuit integrity for failures
not detected due to a double fault in the circuit.
Most PCM failures are caused by internal compo-
nent failures (i.e. relays and solenoids) and shorted
circuits (i.e. pull-ups, drivers, and switched cir-
cuits). These failures are difficult to detect when a
double fault has occurred and only one DTC has
been set.When a PCM (JTEC) and the SKIM are replaced
at the same time, perform the following steps in
order:
(1) Program the new PCM (JTEC).
(2) Program the new SKIM.
(3) Replace all ignition keys and program them to
the new SKIM.
PROGRAMMING THE PCM (JTEC)
The SKIS Secret Key is an ID code that is unique
to each SKIM. This code is programmed and stored
in the SKIM, the PCM, and the ignition key tran-
sponder chip(s). When replacing the PCM, it is nec-
essary to program the secret key into the new PCM
using the DRBIIItscan tool. Perform the following
steps to program the secret key into the PCM.
WJELECTRONIC CONTROL MODULES 8E - 1

(1) Turn the ignition switch to the On position
(transmission in Park/Neutral).
(2) Use the DRBIIItand select THEFT ALARM,
SKIM, then MISCELLANEOUS.
(3) Select PCM REPLACED (GAS ENGINE).
(4) Enter secured access mode by entering the
vehicle four-digit PIN.
(5) Select ENTER to update PCM VIN.
NOTE: If three attempts are made to enter secure
access mode using an incorrect PIN, secured
access mode will be locked out for one hour. To
exit this lockout mode, turn the ignition switch to
the ON position for one hour, then enter the correct
PIN. (Ensure all accessories are turned off. Also
monitor the battery state and connect a battery
charger if necessary).
(6) Press ENTER to transfer the secret key (the
SKIM will send the secret key to the PCM).
(7) Press Page Back to get to the Select System
menu and select ENGINE, MISCELLANEOUS, and
SRI MEMORY CHECK.
(8) The DRBIIItwill ask, ªIs odometer reading
between XX and XX?º Select the YES or NO button
on the DRBIIIt. If NO is selected, the DRBIIItwill
read, ªEnter Odometer Reading (From I.P. odome-
ter)º. Enter the odometer reading from the instru-
ment cluster and press ENTER.
PROGRAMMING THE SKIM
(1) Turn the ignition switch to the On position
(transmission in Park/Neutral).
(2) Use the DRBIIItand select THEFT ALARM,
SKIM, then MISCELLANEOUS.
(3) Select PCM REPLACED (GAS ENGINE).
(4) Program the vehicle four-digit PIN into SKIM.
(5) Select COUNTRY CODE and enter the correct
country.
NOTE: Be sure to enter the correct country code. If
the incorrect country code is programmed into
SKIM, it cannot be changed and the SKIM must be
replaced.
(6) Select YES to update VIN (the SKIM will learn
the VIN from the PCM).
(7) Press ENTER to transfer the secret key (the
PCM will send the secret key to the SKIM).
(8) Program ignition keys to the SKIM.
NOTE: If the PCM and the SKIM are replaced at the
same time, all vehicle ignition keys will need to be
replaced and programmed to the new SKIM.
PROGRAMMING IGNITION KEYS TO THE SKIM
(1) Turn the ignition switch to the On position
(transmission in Park/Neutral).
(2) Use the DRBIIItand select THEFT ALARM,
SKIM, then MISCELLANEOUS.
(3) Select PROGRAM IGNITION KEY'S.
(4) Enter secured access mode by entering the
vehicle four-digit PIN.
NOTE: A maximum of eight keys can be learned to
each SKIM. Once a key is learned to a SKIM it (the
key) cannot be transferred to another vehicle.
(5) Obtain ignition keys to be programmed from
the customer (8 keys maximum).
(6) Using the DRBIIIt, erase all ignition keys by
selecting MISCELLANEOUS, and ERASE ALL CUR-
RENT IGN. KEYS.
(7) Program all of the ignition keys.
If ignition key programming is unsuccessful, the
DRBIIItwill display one of the following messages:
²Programming Not Attempted- The DRBIIIt
attempts to read the programmed key status and
there are no keys programmed into SKIM memory.
²Programming Key Failed (Possible Used
Key From Wrong Vehicle)- SKIM is unable to pro-
gram an ignition key transponder due to one of the
following:
²The ignition key transponder is faulty.
²The ignition key transponder is or has been
already programmed to another vehicle.
²8 Keys Already Learned, Programming Not
Done- The SKIM transponder ID memory is full.
²Learned Key In Ignition- The ID for the igni-
tion key transponder currently in the ignition lock
cylinder is already programmed in SKIM memory.
ADJUSTABLE PEDALS
MODULE
REMOVAL
(1) Disconnect the negative battery cable.
(2) Remove the cluster bezel (Refer to 23 - BODY/
INSTRUMENT PANEL/CLUSTER BEZEL - REMOV-
AL).
(3) Remove the steering column opening cover
(Refer to 23 - BODY/INSTRUMENT PANEL/STEER-
ING COLUMN OPENING COVER - REMOVAL).
(4) Remove the adjustable pedal motor for accessi-
bility. (Refer to 5 - BRAKES/HYDRAULIC/MECHAN-
ICAL/PEDAL - REMOVAL).
(5) Remove the two mounting clips from the mod-
ule (Fig. 1).
(6) Disconnect the electrical connector.
(7) Remove the adjustable pedal module.
8E - 2 ELECTRONIC CONTROL MODULESWJ
ELECTRONIC CONTROL MODULES (Continued)