2003 JEEP GRAND CHEROKEE ABS REAR SENSOR

G-SWITCH
DESCRIPTION
The G-switch (Fig. 4) is located under the rear
seat. The switch has directional arrow and must be
mounted with the arrow pointing towards the front
of the vehicle.
OPERATION
The switch is monitored by the CAB at all times.
The switch contains three mercury switches which
monitor vehicle deceleration rates (G-force). Sudden
changes in deceleration rates trigger the switch,
sending a signal to the CAB.
REMOVAL
(1) Fold the rear seat bottom assembly up for
access to the switch.
(2) Lift up the carpeting and disconnect the switch
harness (Fig. 5).
(3) Remove the switch mounting bolts and remove
the switch.
INSTALLATION
CAUTION: The mercury switch (inside the
G-Switch), will not function properly if the switch is
installed incorrectly. Verify that the switch locating
arrow is pointing to the front of the vehicle (Fig. 6).
(1) Note the position of the locating arrow on the
switch. Position the switch so the arrow faces for-
ward.
(2) Install the switch and tighten the mounting
bolts to 5.6 N´m (50 in. lbs.).
Fig. 2 Left Sensor Connector
1 - LEFT FRONT WHEEL SPEED SENSOR CONNECTOR
2 - ENGINE EXHAUST PIPE
3 - LEFT FRONT FRAME RAIL
4 - FRONT DRIVESHAFT
Fig. 3 Right Sensor Connector
1 - RIGHT FRONT WHEEL SPEED SENSOR CONNECTOR
2 - ENGINE EXHAUST Y-PIPE
3 - RIGHT FRONT FRAME RAIL
4 - RIGHT LOWER SUSPENSION ARM
Fig. 4 G-Switch
1 - SWITCH PART NUMBER
2 - ARROW INDICATES FRONT OF SWITCH FOR PROPER
MOUNTING
5 - 44 BRAKES - ABSWJ
FRONT WHEEL SPEED SENSOR (Continued)

(3) Connect the harness to the switch. Be sure the
harness connector is firmly seated.
(4) Place the carpet in position and fold the rear
seat back down.
REAR WHEEL SPEED SENSOR
DESCRIPTION
A wheel speed sensor is used at each wheel. The
front sensors are mounted to the steering knuckles.The rear sensors are mounted at the outboard end of
the axle. Tone wheels are mounted to the outboard
ends of the front and rear axle shafts. The gear type
tone wheel serves as the trigger mechanism for each
sensor.
OPERATION
The sensors convert wheel speed into a small digi-
tal signal. The CAB sends 12 volts to the sensors.
The sensor has an internal magneto resistance
bridge that alters the voltage and amperage of the
signal circuit. This voltage and amperage is changed
by magnetic induction when the toothed tone wheel
passes the wheel speed sensor. This digital signal is
sent to the CAB. The CAB measures the voltage and
amperage of the digital signal for each wheel.
REMOVAL
(1) Raise and fold the rear seat forward. Then
move the carpeting aside for access to the rear sensor
connectors.
(2) Disconnect the rear sensor wire at the harness
connectors (Fig. 7).
(3) Push the sensor wires and grommets through
the floorpan holes.
(4) Raise and support the vehicle.
(5) Disengage the sensor wire from the axle and
the chassis brackets and from the brake line retain-
ers.
(6) Remove the sensor mounting bolt from the rear
brake backing plate. (Fig. 8).
(7) Remove the sensor from the backing plate.
Fig. 5 G-Switch Mounting
1 - MOUNTING BOLTS
2 - CONNECTOR
3 - G-SWITCH
Fig. 6 G-Switch
1 - SWITCH PART NUMBER
2 - ARROW INDICATES FRONT OF SWITCH FOR PROPER
MOUNTING
Fig. 7 Rear Sensor Connector
1 - RIGHT REAR WHEEL SPEED SENSOR CONNECTOR
2 - LEFT REAR WHEEL SPEED SENSOR CONNECTOR
3 - G-SWITCH SENSOR
4 - PARKING BRAKE CABLES
WJBRAKES - ABS 5 - 45
G-SWITCH (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)

PRESSURE HOLD
Both solenoid valves are closed in the pressure
hold cycle. Fluid apply pressure in the control chan-
nel is maintained at a constant rate. The CAB main-
tains the hold cycle until sensor inputs indicate a
pressure change is necessary.
PRESSURE INCREASE
The inlet valve is open and the outlet valve is
closed during the pressure increase cycle. The pres-
sure increase cycle is used to counteract unequal
wheel speeds. This cycle controls re-application of
fluid apply pressure due to changing road surfaces or
wheel speed.
REMOVAL
(1) Remove the negative battery cable from the
battery.
(2) Remove the air cleaner housing,(Refer to 9 -
ENGINE/AIR INTAKE SYSTEM/AIR CLEANER
HOUSING - REMOVAL).
(3) Pull the CAB harness connector release up and
remove connector (Fig. 10).(4) Remove the brake lines from the HCU.
(5) Remove the HCU/CAB side mounting bolt and
the two rear mounting bolts. (Fig. 11).
(6) Remove the HCU/CAB assembly from the vehi-
cle.
INSTALLATION
(1) Install HCU/CAB assembly into the mounting
bracket and tighten mounting bolts to 12 N´m (9 ft.
lbs.).
(2) Install the brake lines to the HCU and tighten
to 16 N´m (12 ft. lbs.).
(3) Install CAB harness connector and push down
connector release.
(4) Install air cleaner housing,(Refer to 9 -
ENGINE/AIR INTAKE SYSTEM/AIR CLEANER
HOUSING - INSTALLATION).
(5) Install negative battery cable to the battery.
(6) Bleed base and ABS brake systems,(Refer to 5 -
BRAKES - STANDARD PROCEDURE) OR (Refer to
5 - BRAKES - STANDARD PROCEDURE).
Fig. 10 CAB Connector Release
1 - CONNECTOR RELEASE
2 - CAB
Fig. 11 HCU/CAB Assembly
1 - SIDE MOUNTING BOLT
2 - REAR MOUNTING BOLTS
WJBRAKES - ABS 5 - 47
HCU (HYDRAULIC CONTROL UNIT) (Continued)

²Malfunction indicator lamp (Check engine lamp).
Driven through J1850 circuits.
²Overdrive indicator lamp (if equipped). Driven
through J1850 circuits.
²Oxygen sensor heater relays (if equipped).
²Radiator cooling fan relay (pulse width modu-
lated)
²Speed control source
²Speed control vacuum solenoid
²Speed control vent solenoid
²Tachometer (if equipped). Driven through J1850
circuits.
²Transmission convertor clutch circuit
²Transmission 3±4 shift solenoid
²Transmission relay
²Transmission temperature lamp (if equipped)
²Transmission variable force solenoid
OPERATION - 5 VOLT SUPPLIES
Primary 5±volt supply:
²supplies the required 5 volt power source to the
Crankshaft Position (CKP) sensor.
²supplies the required 5 volt power source to the
Camshaft Position (CMP) sensor.
²supplies a reference voltage for the Manifold
Absolute Pressure (MAP) sensor.
²supplies a reference voltage for the Throttle
Position Sensor (TPS) sensor.
Secondary 5±volt supply:
²supplies the required 5 volt power source to the
oil pressure sensor.
²supplies the required 5 volt power source for the
Vehicle Speed Sensor (VSS) (if equipped).
²supplies the 5 volt power source to the transmis-
sion pressure sensor (if equipped with an RE auto-
matic transmission).
OPERATION - IGNITION CIRCUIT SENSE
The ignition circuit sense input tells the PCM the
ignition switch has energized the ignition circuit.
Battery voltage is also supplied to the PCM
through the ignition switch when the ignition is in
the RUN or START position. This is referred to as
the9ignition sense9circuit and is used to9wake up9
the PCM.
REMOVAL
USE THE DRBIIItSCAN TOOL TO REPRO-
GRAM THE NEW POWERTRAIN CONTROL
MODULE (PCM) WITH THE VEHICLES ORIGI-
NAL IDENTIFICATION NUMBER (VIN) AND
THE VEHICLES ORIGINAL MILEAGE. IF THIS
STEP IS NOT DONE, A DIAGNOSTIC TROUBLE
CODE (DTC) MAY BE SET.
The PCM is located on the cowl panel in right/rear
side of engine compartment (Fig. 12).The PCM is located on the cowl panel in right/rear
side of engine compartment (Fig. 12).
To avoid possible voltage spike damage to PCM,
ignition key must be off, and negative battery cable
must be disconnected before unplugging PCM connec-
tors.
(1) Disconnect negative battery cable at battery.
Fig. 12 Powertrain Control Module (PCM) Location
1 - PCM
2 - COOLANT TANK
Fig. 13 Powertrain Control Module (PCM) 32±Way
Connectors
1 - 3 32±WAY CONNECTORS
2 - PCM/BRACKET ASSEMBLY
3 - BRACKET NUTS (3)
8E - 16 ELECTRONIC CONTROL MODULESWJ
POWERTRAIN CONTROL MODULE (Continued)

(5) Pull the upper mounting tabs of the instrument
cluster downward, then pull the instrument cluster
rearward far enough to access the instrument panel
wire harness connector for the instrument cluster
(Fig. 3).
(6) Disconnect the instrument panel wire harness
connector for the instrument cluster from the connec-
tor receptacle on the back of the instrument cluster
housing.
(7) Remove the instrument cluster from the instru-
ment panel.
DISASSEMBLY
Some of the components for the instrument cluster
used in this vehicle are serviced individually. The
serviced components include: the incandescent
instrument cluster indicator and illumination lamp
bulbs (including the integral bulb holders), the clus-
ter lens, hood and mask unit, and the cluster housing
rear cover. Following are the procedures for disas-
sembling these components from the instrument clus-
ter unit.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE SUPPLEMENTAL RESTRAINT
SYSTEM BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, DRIVER AIRBAG,
PASSENGER AIRBAG, SIDE CURTAIN AIRBAG,
FRONT IMPACT SENSOR, SIDE IMPACT SENSOR,
OR INSTRUMENT PANEL COMPONENT DIAGNOSIS
OR SERVICE. DISCONNECT AND ISOLATE THE
BATTERY NEGATIVE (GROUND) CABLE, THEN
WAIT TWO MINUTES FOR THE SYSTEM CAPACI-TOR TO DISCHARGE BEFORE PERFORMING FUR-
THER DIAGNOSIS OR SERVICE. THIS IS THE ONLY
SURE WAY TO DISABLE THE SUPPLEMENTAL
RESTRAINT SYSTEM. FAILURE TO TAKE THE
PROPER PRECAUTIONS COULD RESULT IN ACCI-
DENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY.
WARNING: ON VEHICLES EQUIPPED WITH THE
PREMIUM INSTRUMENT CLUSTER, THE CLUSTER
CIRCUITRY PROVIDES AN ALTERNATING CURRENT
TO SUPPLY POWER TO THE ELECTRO-LUMINES-
CENT ILLUMINATION LAMP THROUGH A PIGTAIL
WIRE AND CONNECTOR THAT IS ACCESSIBLE AT
THE BACK OF THE CLUSTER HOUSING. USE
PROPER PRECAUTIONS WHEN HANDLING THIS
UNIT DURING DIAGNOSIS OR SERVICE TO AVOID
ELECTRICAL SHOCK AND POSSIBLE PERSONAL
INJURY.
CLUSTER BULB
This procedure applies to each of the incandescent
cluster illumination lamp or indicator bulb and bulb
holder units. However, the illumination lamps and
the indicators use different bulb and bulb holder unit
sizes. They must never be interchanged. Be certain
that any bulb holder removed from the electronic cir-
cuit board is reinstalled in the correct position.
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the instrument cluster from the instru-
ment panel. (Refer to 8 - ELECTRICAL/INSTRU-
MENT CLUSTER - REMOVAL).
(3) Turn the bulb holder counterclockwise about
sixty degrees on the cluster electronic circuit board
(Fig. 4).
(4) Pull the bulb and bulb holder straight back to
remove it from the bulb mounting hole in the cluster
electronic circuit board.
CLUSTER LENS, HOOD AND MASK
(1) Disconnect and isolate the battery negative
cable.
(2) Remove the instrument cluster from the instru-
ment panel. (Refer to 8 - ELECTRICAL/INSTRU-
MENT CLUSTER - REMOVAL).
(3) Work around the perimeter of the cluster hous-
ing to disengage each of the eight latches that secure
the cluster lens, hood and mask unit to the cluster
housing (Fig. 5).
(4) Gently pull the cluster lens, hood and mask
unit away from the cluster housing.
CLUSTER HOUSING REAR COVER
(1) Disconnect and isolate the battery negative
cable.
Fig. 3 Instrument Cluster Remove/Install
1 - INSTRUMENT PANEL WIRE HARNESS CONNECTOR
2 - INSTRUMENT CLUSTER
8J - 10 INSTRUMENT CLUSTERWJ
INSTRUMENT CLUSTER (Continued)

(4) Turn the ignition switch to the Off position.
Check for continuity between the ground circuit cav-
ity of the overhead wire harness connector for the
automatic day/night mirror and a good ground. There
should be continuity. If OK, go to Step 5. If not OK,
repair the open ground circuit to ground as required.
(5) Turn the ignition switch to the On position. Set
the parking brake. Place the transmission gear selec-
tor lever in the Reverse position. Check for battery
voltage at the backup lamp switch output circuit cav-
ity of the overhead wire harness connector for the
automatic day/night mirror. If OK, reconnect the
overhead wire harness connector to the automatic
day/night mirror connector receptacle and go to Step
6. If not OK, repair the open backup lamp switch
output circuit as required.
(6) Place the transmission gear selector lever in
the Neutral position. Place the automatic day/night
mirror switch in the Auto (LED next to the switch is
lighted) position (Fig. 1). Cover the forward facing
ambient photocell sensor to keep out any ambient
light.
NOTE: The ambient photocell sensor must be cov-
ered completely, so that no light reaches the sen-
sor. Use a finger pressed tightly against the sensor,
or cover the sensor completely with electrical tape.
(7) Shine a light into the rearward facing head-
lamp photocell sensor. The automatic day/night mir-
ror should darken. If OK, go to Step 8. If not OK,
replace the faulty automatic day/night mirror unit.
(8) With the mirror darkened, place the transmis-
sion gear selector lever in the Reverse position. The
automatic day/night mirror should return to its nor-
mal reflectance. If not OK, replace the faulty auto-
matic day/night mirror unit.POWER FOLD-AWAY MIRROR -
EXPORT
DESCRIPTION
Some vehicles are equipped with Power Fold-Away
Side View Mirrors. This feature allows both the
driver and passenger side view mirrors to fold
inward (retract) on demand. This feature is con-
trolled by an additional switch located on the power
mirror switch.
The fold-away side view mirror is attached to the
vehicle's door in the same manner as mirrors without
the fold-away option. The fold-away mirrors unique
option is the internal motor which allows the mirrors
to fold inward on demand. the fold-away mirror
motor is not serviceable separately, and if a motor is
found to be faulty the entire side view mirror must
be replaced.
OPERATION
When the mirror retract switch is depressed, both
of the side view mirrors will fold inward, thus mak-
ing the overall width of the vehicle the smallest pos-
sible. This can be very helpful where parking space is
an absolute minimum.
DIAGNOSIS AND TESTING - POWER
FOLD-AWAY MIRROR - EXPORT
The most reliable, efficient and accurate means to
diagnose the power mirror system requires the use of
a DRB scan tool and the proper Diagnostic Proce-
dures manual. The DRB scan tool can provide confir-
mation that the PCI data bus is functional, that all
of the electronic modules are sending and receiving
the proper messages on the PCI data bus, that the
power mirror motors are being sent the proper hard
wired outputs, and that the mirror position potenti-
ometers are returning the proper outputs to the door
modules for them to perform their power mirror sys-
tem functions.
REMOVAL
The fold-away mirror motor is not serviceable sep-
arately, and if a motor is found to be faulty the entire
side view mirror must be replaced. (Refer to 8 -
ELECTRICAL/POWER MIRRORS/SIDEVIEW MIR-
ROR - REMOVAL).
Fig. 1 Automatic Day/Night Mirror
1 - LED INDICATOR
2 - SWITCH
3 - HEADLAMP SENSOR
8N - 14 POWER MIRRORSWJ
AUTOMATIC DAY/NIGHT MIRROR (Continued)

Typically, both initiators are used during an airbag
deployment event. However, it is possible for only one
initiator to be used during a deployment due to an
airbag system fault; therefore, it is necessary to
always confirm that both initiators have been used in
order to avoid the improper disposal of potentially
live pyrotechnic materials. (Refer to 8 - ELECTRI-
CAL/RESTRAINTS - STANDARD PROCEDURE -
SERVICE AFTER A SUPPLEMENTAL RESTRAINT
DEPLOYMENT).
REMOVAL
The following procedure is for replacement of a
faulty or damaged passenger airbag. If the airbag is
faulty or damaged, but not deployed, review the rec-
ommended procedures for handling non-deployed
supplemental restraints. (Refer to 8 - ELECTRICAL/
RESTRAINTS - STANDARD PROCEDURE - HAN-
DLING NON-DEPLOYED SUPPLEMENTAL
RESTRAINTS). If the passenger airbag has been
deployed, review the recommended procedures for
service after a supplemental restraint deployment
before removing the airbag from the vehicle. (Refer to
8 - ELECTRICAL/RESTRAINTS - STANDARD PRO-
CEDURE - SERVICE AFTER A SUPPLEMENTAL
RESTRAINT DEPLOYMENT).
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE SUPPLEMENTAL RESTRAINT
SYSTEM BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, DRIVER AIRBAG,
PASSENGER AIRBAG, FRONT IMPACT SENSOR,
SIDE IMPACT SENSOR, SIDE CURTAIN AIRBAG, OR
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. DISCONNECT AND ISOLATE THE BAT-
TERY NEGATIVE (GROUND) CABLE, THEN WAIT
TWO MINUTES FOR THE SYSTEM CAPACITOR TO
DISCHARGE BEFORE PERFORMING FURTHER
DIAGNOSIS OR SERVICE. THIS IS THE ONLY SURE
WAY TO DISABLE THE SUPPLEMENTAL
RESTRAINT SYSTEM. FAILURE TO TAKE THE
PROPER PRECAUTIONS COULD RESULT IN ACCI-
DENTAL AIRBAG DEPLOYMENT AND POSSIBLE
PERSONAL INJURY.
WARNING: WHEN REMOVING A DEPLOYED AIR-
BAG, RUBBER GLOVES, EYE PROTECTION, AND A
LONG-SLEEVED SHIRT SHOULD BE WORN. THERE
MAY BE DEPOSITS ON THE AIRBAG UNIT AND
OTHER INTERIOR SURFACES. IN LARGE DOSES,
THESE DEPOSITS MAY CAUSE IRRITATION TO THE
SKIN AND EYES.(1) Disconnect and isolate the battery negative
cable. Wait two minutes for the system capacitor to
discharge before further service.
(2) Remove the top pad from the instrument panel.
(Refer to 23 - BODY/INSTRUMENT PANEL/IN-
STRUMENT PANEL TOP PAD - REMOVAL).
(3) Disconnect the passenger airbag pigtail wire
connector from the instrument panel wire harness
connector for the airbag. This connector is secured to
the outside of the outboard airbag unit end bracket.
To disconnect the connector:
(a) Slide the red Connector Position Assurance
(CPA) lock on the top of the connector toward the
side of the connector.
(b) Depress the connector latch tab and pull the
two halves of the connector straight away from
each other.
(4) Remove the two screws that secure the two air-
bag end bracket front mounting tabs to the top of the
instrument panel structural duct (Fig. 32).
(5) Remove the two screws that secure the two air-
bag end bracket rear mounting tabs to the rear of the
structural duct, just above the instrument panel
upper glove box opening reinforcement.
(6) Remove the passenger airbag from the instru-
ment panel structural duct as a unit.
Fig. 32 Passenger Side Airbag Module Remove/
Install
1 - STRUCTURAL DUCT
2 - PASSENGER AIRBAG
3 - WIRE HARNESS CONNECTOR
4 - STRUCTURAL DUCT
5 - SCREWS
WJRESTRAINTS 8O - 31
PASSENGER AIRBAG (Continued)