2002 JEEP LIBERTY Engine

HEADLAMP BULB
REMOVAL
NORTH AMERICA
(1) Disconnect and isolate the battery negative
cable.
(2) Reach behind the headlamp unit from the
engine compartment side of the upper radiator cross-
member to access the headlamp bulb lock ring (Fig.
23).
(3) Firmly grasp the lock ring on the back of the
headlamp unit housing.
(4) Rotate the lock ring on the back of the head-
lamp unit housing counterclockwise about 30
degrees.
CAUTION: Do not contaminate the bulb glass by
touching it with your fingers or by allowing it to
contact other oily surfaces. Shortened bulb life will
result.
(5) Pull the lock ring, socket, and bulb straight out
of the headlamp unit housing and up from behind
the upper radiator crossmember (Fig. 24).
(6) Disconnect the grille opening reinforcement
wire harness connector for the headlamp bulb from
the connector receptacle on the bulb socket.
(7) Remove the bulb and bulb socket from the lock
ring as a unit.
REST-OF-WORLD
(1) Disconnect and isolate the battery negative
cable.(2) Remove the headlamp unit from the grille
opening reinforcement. (Refer to 8 - ELECTRICAL/
LAMPS/LIGHTING - EXTERIOR/HEADLAMP UNIT
- REMOVAL).
(3) Firmly grasp the tab of the headlamp boot seal
on the back of the headlamp unit housing (Fig. 25).
(4) Pull the tab away from the back of the head-
lamp unit housing to remove the boot seal from the
housing and the bulb base.
Fig. 23 Headlamp Bulb Lock Ring
1 - HEADLAMP UNIT HOUSING
2 - LOCK RING
3 - SOCKET & BULB
Fig. 24 Headlamp Bulb Remove/Install
1 - HEADLAMP BULB
2 - SOCKET
3 - LOCK RING
Fig. 25 Headlamp Bulb Boot Seal Remove
1 - LEVELING MOTOR (IF EQUIPPED)
2 - BOOT SEAL
3 - FRONT POSITION LAMP
4 - ADJUSTING SCREW
5-TAB
6 - BULB BASE
KJLAMPS/LIGHTING - EXTERIOR 8L - 31

²Trailer Tow Adapter- Vehicles equipped with
a factory-installed trailer towing package have an
adapter provided that adapts the factory-installed
heavy duty 7-way trailer tow connector to a conven-
tional 4-way light duty connector.
²Trailer Tow Connector- Vehicles equipped
with a factory-installed trailer towing package have a
heavy duty 7-way trailer tow connector installed in a
bracket on the trailer hitch receiver.
²Trailer Tow Relays- Vehicles equipped with a
factory-installed trailer towing package have a con-
nector bank containing four relays located behind the
right quarter trim panel and over the right rear
wheel housing. The four relays are used to supply
fused ignition switch output (run), brake lamps, right
turn signal, and left turn signal outputs to a trailer
through the trailer tow wiring and connectors.
Hard wired circuitry connects the exterior lighting
system components to the electrical system of the
vehicle. These hard wired circuits are integral to sev-
eral wire harnesses, which are routed throughout the
vehicle and retained by many different methods.
These circuits may be connected to each other, to the
vehicle electrical system and to the exterior lighting
system components through the use of a combination
of soldered splices, splice block connectors, and many
different types of wire harness terminal connectors
and insulators. Refer to the appropriate wiring infor-
mation. The wiring information includes wiring dia-
grams, proper wire and connector repair procedures,
further details on wire harness routing and reten-
tion, as well as pin-out and location views for the
various wire harness connectors, splices and grounds.
OPERATION
Following are paragraphs that briefly describe the
operation of each of the major exterior lighting sys-
tems. The hard wired circuits and components of the
exterior lighting systems may be diagnosed and
tested using conventional diagnostic tools and proce-
dures. However, conventional diagnostic methods
may not prove conclusive in the diagnosis of the Body
Control Module (BCM), the ElectroMechanical
Instrument Cluster (EMIC), the Powertrain Control
Module (PCM), or the Programmable Communica-
tions Interface (PCI) data bus network. The most
reliable, efficient, and accurate means to diagnose
the BCM, the EMIC, the PCM, and the PCI data bus
network inputs and outputs related to the various
exterior lighting systems requires the use of a
DRBIIItscan tool. Refer to the appropriate diagnos-
tic information.BACKUP LAMPS
The backup (or reverse) lamps have a path to
ground at all times through their connection to the
rear lighting wire harness from a take out of the rear
body wire harness with an eyelet terminal connector
that is secured by a ground screw to the base of the
right D-pillar behind the quarter trim panel. The
backup lamps receive battery current from a fused
ignition switch output (run) fuse in the Junction
Block (JB) on the back-up lamp feed circuit only
when the backup lamp switch (manual transmission),
or backup lamp switch circuit of the Transmission
Range Sensor (TRS - electronic automatic transmis-
sion) is closed by the gearshift mechanism within the
transmission.
BRAKE LAMPS
The brake (or stop) lamps have a path to ground at
all times through their connection to the rear light-
ing wire harness from a take out of the rear body
wire harness with an eyelet terminal connector that
is secured by a screw to the base of the right D-pillar
behind the quarter trim panel. The Center High
Mounted Stop Lamp (CHMSL) has a path to ground
at all times through its connection to the rear body
wire harness from a take out of the rear body wire
harness with an eyelet terminal connector that is
secured by a ground screw to the driver side D-pillar
(left side D-pillar for left-hand drive, right side D-pil-
lar for right-hand drive) behind the quarter trim
panel. The brake lamps and CHMSL receive battery
current from a fused B(+) fuse in the Junction Block
(JB) on the brake lamp switch output circuit only
when the brake lamp switch circuit of the brake
lamp switch is closed by the brake pedal arm.
DAYTIME RUNNING LAMPS
Vehicles manufactured for sale in Canada illumi-
nate the high beam filament at a reduced intensity
when the engine is running and the exterior lamps
are turned off. This feature is enabled by the Body
Control Module (BCM) and a solid state Daytime
Running Lamps (DRL) relay, which is installed in the
Junction Block (JB) and the high beam relay is omit-
ted. When the BCM monitors an engine speed signal
of greater than 450 RPM and the status of the exte-
rior lighting switch input from the multi-function
switch is Off, the BCM duty cycles the DRL relay to
produce illumination of the headlamp high beam fil-
aments at a reduced intensity. The BCM also pro-
vides normal headlamp high beam operation through
the DRL relay on vehicles so equipped. When the
DRL relay is energized, it provides battery current
from a fused B(+) fuse in the JB to the headlamp
high beam filament through the DRL relay output
circuit.
KJLAMPS8Ls-5
LAMPS/LIGHTING - EXTERIOR (Continued)

FRONT FOG LAMPS
Vehicles equipped with optional front fog lamps
have a premium Body Control Module (BCM), a front
fog lamp relay installed in the Junction Block (JB),
and a front fog lamp switch integral to the left (light-
ing) control stalk of the multi-function switch. The
front fog lamps have a path to ground at all times
through their connection to the front fascia wire har-
ness from two take outs of the headlamp and dash
wire harness with eyelet terminal connectors that
are secured by ground screws to the left inner fender
shield in the engine compartment. The BCM controls
front fog lamp operation by monitoring the exterior
lighting switch input from the multi-function switch,
then energizing or de-energizing the front fog lamp
relay control coil; and, by sending the appropriate
electronic message to the instrument cluster over the
Programmable Communications Interface (PCI) data
bus to turn the front fog lamp indicator on or off.
When the front fog lamp relay is energized, it pro-
vides battery current from a fused B(+) fuse in the
JB to the front fog lamps through the front fog lamp
relay output circuit. The BCM provides a battery
saver (load shedding) feature for the front fog lamps,
which will turn these lamps off if they are left on for
more than about eight minutes with the ignition
switch in the Off position. In certain markets where
required, the front fog lamps are also turned off by
the BCM whenever the headlamp high beams are
selected. Each front fog lamp includes an integral
adjustment screw to be used for static aiming the fog
lamp beams.
HAZARD WARNING LAMPS
With the hazard switch in the On position, the
hazard warning system is activated causing the haz-
ard switch button illumination lamp, the right and
left turn signal indicators, and the right and left turn
signal lamps to flash on and off. When the hazard
warning system is activated, the circuitry within the
hazard switch and electronic combination flasher
unit will repeatedly energize and de-energize two
internal relays that switch battery current from a
fused B(+) fuse in the Junction Block (JB) to the
right side and left side turn signal indicators, and
turn signal lamps through the right and left turn sig-
nal circuits. The flashing of the hazard switch button
illumination lamp is performed internally by the haz-
ard switch and combination flasher unit circuit
board. The hazard warning lamps can also be ener-
gized by the Body Control Module (BCM) through a
hazard lamp control circuit input to the hazard
switch and combination flasher unit.HEADLAMPS
The headlamp system includes the Body Control
Module (BCM), a low beam relay installed in the
Junction Block (JB), a high beam relay installed in
the JB (except Canada), a solid state Daytime Run-
ning Lamps (DRL) relay installed in the JB (Canada
only), and the exterior lighting (headlamp and dim-
mer) switches integral to the left (lighting) control
stalk of the multi-function switch. The headlamp
bulbs have a path to ground at all times through
their connection to the grille opening reinforcement
wire harness from two take outs of the headlamp and
dash wire harness with eyelet terminal connectors
that are secured by ground screws to the left inner
fender shield in the engine compartment. The BCM
controls the headlamp operation by monitoring the
exterior lighting switch inputs from the multi-func-
tion switch, then energizing or de-energizing the con-
trol coils of the low beam relay, the high beam relay,
or the solid state circuitry of the DRL relay; and, by
sending the appropriate electronic message to the
instrument cluster over the Programmable Commu-
nications Interface (PCI) data bus to turn the high
beam indicator on or off. When each respective relay
is energized, it provides battery current from a fused
B(+) fuse in the Power Distribution Center (PDC)
through a relay (low beam, high beam, or DRL) out-
put circuit and four separate fuses in the JB through
individual fused right and left, low and high beam
output circuits to the appropriate headlamp bulb fil-
aments. The BCM provides a battery saver (load
shedding) feature for the headlamps, which will turn
these lamps off if they are left on for more than
about eight minutes with the ignition switch in the
Off position; and, a headlamp delay feature with a
DRBIIItscan tool programmable delay interval.
Each headlamp includes an integral adjustment
screw to be used for static aiming of the headlamp
beams.
HEADLAMP LEVELING
In certain markets where required, a headlamp
leveling system is provided on the vehicle. The head-
lamp leveling system includes unique headlamp units
equipped with a headlamp leveling actuator motor,
and a rotary thumbwheel actuated headlamp leveling
switch on the instrument panel. The headlamp level-
ing system allows the headlamp beams to be
adjusted to one of four vertical positions to compen-
sate for changes in inclination caused by the loading
of the vehicle suspension. The actuator motors are
mechanically connected through an integral pushrod
to an adjustable headlamp reflector. The headlamp
leveling switch is a resistor multiplexed unit that
provides one of four voltage outputs to the headlamp
leveling motors. The headlamp leveling motors will
8Ls - 6 LAMPSKJ
LAMPS/LIGHTING - EXTERIOR (Continued)

move the headlamps to the selected position based
upon the voltage input received from the switch. The
headlamp leveling motors and switch have a path to
ground at all times. The headlamp leveling compo-
nents operate on battery current received through
the fused park lamp relay output circuit so that the
system will only operate when the exterior lighting is
turned on.
PARK LAMPS
The park lamps system includes the Body Control
Module (BCM), a park lamp relay installed in the
Junction Block (JB), and the exterior lighting switch
integral to the left (lighting) control stalk of the
multi-function switch. The front park lamp and side
marker or, if equipped, the front position lamp bulbs
each have a path to ground at all times through their
connections to the grille opening reinforcement wire
harness from two take outs of the headlamp and
dash wire harness with eyelet terminal connectors
that are secured by ground screws to the left inner
fender shield in the engine compartment. The rear
park lamp bulbs and license plate lamp have a path
to ground at all times through their connection to the
rear lighting wire harness from a take out of the rear
body wire harness with an eyelet terminal connector
that is secured by a ground screw to the base of the
right D-pillar behind the quarter trim panel. The
BCM controls the park lamp operation by monitoring
the exterior lighting switch inputs from the multi-
function switch, then energizing or de-energizing the
control coil of the park lamp relay. When the park
lamp relay is energized, it provides battery current
from a fused B(+) fuse in the Power Distribution
Center (PDC) through a park lamp relay output cir-
cuit and a separate fuse in the JB through a fused
park lamp relay output circuit to the appropriate
lamp bulb filaments. The BCM provides a battery
saver (load shedding) feature for the park lamps,
which will turn these lamps off if they are left on for
more than about eight minutes with the ignition
switch in the Off position.
REAR FOG LAMPS
Rear fog lamps are installed on vehicles manufac-
tured for certain markets where they are required.
The rear fog lamp system includes a premium Body
Control Module (BCM), a rear fog lamp relay
installed in the Junction Block (JB), and a rear fog
lamp switch integral to the left (lighting) control
stalk of the multi-function switch. The rear fog lamps
have a path to ground at all times through their con-
nection to the rear lighting wire harness from a take
out of the rear body wire harness with an eyelet ter-
minal connector that is secured by a ground screw to
the base of the right D-pillar behind the quarter trimpanel. The BCM controls rear fog lamp operation by
monitoring the exterior lighting switch input from
the multi-function switch, then energizing or de-ener-
gizing the rear fog lamp relay control coil; and, by
sending the appropriate electronic message to the
instrument cluster over the Programmable Commu-
nications Interface (PCI) data bus to turn the rear
fog lamp indicator on or off. When the rear fog lamp
relay is energized, it provides battery current from a
fused B(+) fuse in the JB to the rear fog lamps
through the rear fog lamp relay output circuit. The
BCM provides a battery saver (load shedding) feature
for the rear fog lamps, which will turn these lamps
off if they are left on for more than about eight min-
utes with the ignition switch in the Off position.
TURN SIGNAL LAMPS
When the left control stalk of the multi-function
switch is moved up (right turn) or down (left turn),
the turn signal system is activated causing the
selected right or left turn signal indicator, and right
or left turn signal lamps to flash on and off. When
the turn signal system is activated, the circuitry
within the turn signal switch and the hazard switch/
electronic combination flasher unit will repeatedly
energize and de-energize one of two internal relays
that switch battery current from a fused ignition
switch output (run) fuse in the Junction Block (JB) to
the right side or left side turn signal indicators and
turn signal lamps through the right or left turn sig-
nal circuits. The ElectroMechanical Instrument Clus-
ter (EMIC) chime tone generator will generate an
audible turn signal cancel warning each time the
vehicle is driven for a distance of about 3.2 kilome-
ters (about two miles) with a turn signal indicator
flashing. The EMIC uses Programmable Communica-
tions Interface (PCI) data bus distance messages
from the Powertrain Control Module (PCM) and a
hard wired input from the turn signal switch cir-
cuitry of the multi-function switch to determine when
to sound the turn signal cancel warning.
DIAGNOSIS AND TESTING - LAMPS/LIGHTING
- EXTERIOR
The hard wired circuits and components of the
exterior lighting systems may be diagnosed and
tested using conventional diagnostic tools and proce-
dures. However, conventional diagnostic methods
may not prove conclusive in the diagnosis of the Body
Control Module (BCM), the ElectroMechanical
Instrument Cluster (EMIC), the Powertrain Control
Module (PCM), or the Programmable Communica-
tions Interface (PCI) data bus network. The most
reliable, efficient, and accurate means to diagnose
the BCM, the EMIC, the PCM, and the PCI data bus
network inputs and outputs related to the various
KJLAMPS8Ls-7
LAMPS/LIGHTING - EXTERIOR (Continued)

SPECIFICATIONS - LAMPS/LIGHTING -
EXTERIOR
BULB SPECIFICATIONS
LAMP BULB
Backup 3157 P27/7W
Brake 3157 P27/7W
Center High Mounted
Stop921/W16W
Front Fog 9145
Front Park 3157 P27/7W
Front Position W5W
Front Side Marker 168
Front Turn 3157 P27/7W
Headlamp (North
America)9007QL
Headlamp (Rest-Of-
World)H-4 W0W6
License Plate (North
America)168
License Plate (Rest-Of-
World)W5W
Rear Fog 3157 P27/7W
Rear Park/Tail 3157 P27/7W
Rear Turn 3157 P27/7W
Side Repeater W5W
BACKUP LAMP SWITCH
DESCRIPTION
Vehicles equipped with a manual transmission
have a normally open, spring-loaded plunger type
back-up lamp switch (Fig. 2). The backup lamp
switch is located in a threaded hole on the side of the
manual transmission housing, beneath the floor
panel of the vehicle. The backup lamp switch has a
threaded body and a hex formation near the plunger
end of the switch, and an integral connector recepta-
cle at the opposite end of the switch. When installed,
only the connector receptacle and the hex formation
are visible on the outside of the transmission hous-
ing. Vehicles with an optional electronic automatic
transmission have a Transmission Range Sensor
(TRS) that is used to perform several functions,
including that of the backup lamp switch. The TRS is
described in further detail elsewhere in this service
information. The backup lamp switch cannot be
adjusted or repaired and, if faulty or damaged, the
entire switch unit must be replaced.
OPERATION
The backup lamp switch controls the flow of bat-
tery current to the backup lamp bulbs at the back of
the vehicle through an output on the back-up lamp
feed circuit. The switch plunger is mechanically actu-
ated by the gearshift mechanism within the trans-
mission, which will depress the switch plunger and
close the switch contacts whenever the reverse gear
has been selected. The switch receives battery cur-
rent through a fuse in the Junction Block (JB) on a
fused ignition switch output (run) circuit whenever
the ignition switch is in the On position. A take out
of the engine wire harness connects the backup lamp
switch to the vehicle electrical system. The backup
lamp switch and circuits can be tested using conven-
tional diagnostic tools and methods.
DIAGNOSIS AND TESTING - BACKUP LAMP
SWITCH
(1) Disconnect and isolate the battery negative
cable.
(2) Raise and support the vehicle.
(3) Locate and disconnect the engine wire harness
connector for the backup lamp switch from the
switch connector receptacle.
(4) Check for continuity between the two terminal
pins in the backup lamp switch connector receptacle.
(a) With the gear selector lever in the Reverse
position, there should be continuity.
(b) With the gear selector lever in any position
other than Reverse, there should be no continuity.
Fig. 2 Backup Lamp Switch - Typical
1 - MANUAL TRANSMISSION
2 - BACKUP LAMP SWITCH
3 - ENGINE WIRE HARNESS
KJLAMPS8Ls-15
LAMPS/LIGHTING - EXTERIOR (Continued)

(2) Remove the radio from the instrument panel.
(Refer to 8 - ELECTRICAL/AUDIO/RADIO -
REMOVAL).
(3) Remove the screw at the top of the instrument
panel radio opening that secures the hazard switch
to the instrument panel trim (Fig. 22).
(4) Reach through and above the instrument panel
radio opening to access the two latch tabs of the
stamped metal hazard switch mounting bracket.
(5) Using two fingertips, pull rearward and down-
ward on the latch tabs on the back of the hazard
switch until it is disengaged from the instrument
panel trim.
(6) Push the hazard switch button through the
button opening of the instrument panel far enough to
disengage the alignment pins on each side of the
switch housing from the saddle formations of the two
stanchions on the back of the instrument panel trim,
just below and to either side of the button opening.
(7) Disconnect the instrument panel wire harness
connector for the hazard switch from the switch con-
nector receptacle.
(8) Remove the hazard switch through the instru-
ment panel radio opening.
INSTALLATION
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, DISABLE THE SUPPLEMENTAL RESTRAINT
SYSTEM BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, DRIVER AIRBAG,PASSENGER AIRBAG, SEAT BELT TENSIONER,
FRONT IMPACT SENSORS, SIDE CURTAIN AIRBAG,
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.
(1) Position the hazard switch through the instru-
ment panel radio opening.
(2) Reconnect the instrument panel wire harness
connector for the hazard switch to the switch connec-
tor receptacle.
(3) Reach through and above the instrument panel
radio opening to position the hazard switch for
installation.
(4) Guide the hazard switch button through the
button opening of the instrument panel, which will
engage the alignment pins on each side of the switch
housing with the saddle formations of the two stan-
chions on the back of the instrument panel trim, just
below and to either side of the button opening.
(5) Using hand pressure, press upward on the
back of the hazard switch until the latch tabs of the
mounting bracket on the back of the switch are both
engaged with the instrument panel trim (Fig. 22).
(6) Install and tighten the screw at the top of the
instrument panel radio opening that secures the haz-
ard switch to the instrument panel trim. Tighten the
screw to 2 N´m (17 in. lbs.).
(7) Reinstall the radio into the instrument panel.
(Refer to 8 - ELECTRICAL/AUDIO/RADIO -
INSTALLATION).
(8) Reconnect the battery negative cable.
HEADLAMP BULB
REMOVAL
NORTH AMERICA
(1) Disconnect and isolate the battery negative
cable.
(2) Reach behind the headlamp unit from the
engine compartment side of the upper radiator cross-
member to access the headlamp bulb lock ring (Fig.
23).
(3) Firmly grasp the lock ring on the back of the
headlamp unit housing.
Fig. 22 Hazard Switch Remove/Install
1 - WIRE HARNESS CONNECTOR
2 - HAZARD SWITCH
3 - ALIGNMENT PIN (2)
4 - STANCHION (2)
5 - INSTRUMENT PANEL
6 - SCREW (1)
7 - MOUNTING BRACKET LATCH TAB (2)
8Ls - 30 LAMPSKJ
HAZARD SWITCH (Continued)

NOTE: Individual channels cannot be erased. Eras-
ing the transmitter codes will erase ALL pro-
grammed codes.
STANDARD PROCEDURE - SETTING
TRANSMITTER CODES
(1) Turn off the engine.
(2) Erase the factory test codes by pressing but-
tons 1 and 3. Release the buttons when the two
green lights begin to flash (about 20 seconds).
(3) Choose one of the three buttons to train. Place
the hand-held transmitter within one inch of the uni-
versal transmitter and push the buttons on both
transmitters. The green dot below the house symbol
will begin to flash slowly.
(4) When the red light on the universal transmit-
ter begins to flash rapidly (this may take as long as
60 seconds), release both buttons. Your universal
transmitter is now ªtrainedº. To train the other but-
tons, repeat Step 3 and Step 4. Be sure to keep your
hand-held transmitter in case you need to retrain the
universal transmitter.
AMBIENT TEMP SENSOR
DESCRIPTION
Ambient air temperature is monitored by the Com-
pass Mini-Trip Computer (CMTC) through ambient
temperature sensor messages received from the Body
Control Module (BCM) over the Programmable Com-
munications Interface (PCI) data bus network. The
BCM receives a hard wired input from the ambient
temperature sensor. The ambient temperature sensor
(Fig. 8) is a variable resistor mounted in front the
radiator, behind the grille, near the center of the
vehicle.
Refer toBody Control Modulein Electronic Con-
trol Modules. For complete circuit diagrams, refer to
the appropriate wiring information. The ambient
temperature sensor cannot be adjusted or repaired
and, if faulty or damaged, it must be replaced.
OPERATION
The ambient temperature sensor is a variable
resistor that operates on a five-volt reference signal
sent to it by the BCM. The resistance in the sensor
changes as temperature changes, changing the tem-
perature sensor signal circuit voltage to the BCM.
Based upon the resistance in the sensor, the BCM
senses a specific voltage on the temperature sensor
signal circuit, which it is programmed to correspond
to a specific temperature. The BCM then sends the
proper ambient temperature messages to the CMTC
over the PCI data bus.
The thermometer function is supported by the
ambient temperature sensor, a wiring circuit, the
Body Control Module (BCM), the Programmable
Communications Interface (PCI) data bus, and a por-
tion of the Compass Mini-Trip Computer module.
The ambient temperature sensor circuit can also be
diagnosed by referring toDiagnosis and Testing -
Ambient Temperature Sensor, and Diagnosis
and Testing - Ambient Temperature Sensor Cir-
cuit. If the temperature sensor and circuit are con-
firmed to be OK, but the temperature display is
inoperative or incorrect, refer toDiagnosis and
Testing - Compass Mini-Trip Computerin this
section. For complete circuit diagrams, refer to the
appropriate wiring information.
DIAGNOSIS AND TESTING
DIAGNOSIS AND TESTING - AMBIENT
TEMPERATURE SENSOR
(1) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the ambient temperature sensor wire har-
ness connector.
(2) Measure the resistance of the ambient temper-
ature sensor. At ±40É C (±40É F), the sensor resis-
tance is 336 kilohms. At 55É C (140É F), the sensor
resistance is 2.488 kilohms. The sensor resistance
should read between these two values. If OK, refer to
Diagnosis and Testing - Ambient Temperature
Sensor Circuitin this group. If not OK, replace the
faulty ambient temperature sensor.
DIAGNOSIS AND TESTING - AMBIENT
TEMPERATURE SENSOR CIRCUIT
(1) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Disconnect the ambient temperature sensor wire har-
ness connector and the Body Control Module wire
harness connector.
(2) Connect a jumper wire between the two termi-
nals in the body half of the ambient temperature sen-
sor wire harness connector.
Fig. 8 Ambient Temperature Sensor
KJMESSAGE SYSTEMS 8M - 9
UNIVERSAL TRANSMITTER (Continued)

FRONT IMPACT SENSOR
DESCRIPTION
Two front impact sensors are used on this model,
one each for the left and right sides of the vehicle
(Fig. 17). These sensors are mounted remotely from
the impact sensor that is internal to the Airbag Con-
trol Module (ACM). Each front sensor is secured with
two screws to the backs of the right and left vertical
members of the radiator support within the engine
compartment. The sensor housing has an integral
connector receptacle and two integral mounting
points each with a metal sleeve to provide crush pro-
tection.
The right and left front impact sensors are identi-
cal in construction and calibration with two excep-
tions:
²On models equipped with an optional 2.4L gaso-
line engine, the left front impact sensor includes a
shim that moves the sensor three millimeters toward
the rear of the vehicle on the left vertical member of
the radiator support for additional clearance that is
required for that application.
²On models equipped with an optional diesel
engine, the left front impact sensor includes a
stamped metal mounting bracket that rotates theconnector receptacle end of the sensor toward the
outboard side of the vehicle for additional clearance
that is required for that application.
A cavity in the center of the molded black plastic
impact sensor housing contains the electronic cir-
cuitry of the sensor which includes an electronic com-
munication chip and an electronic impact sensor.
Potting material fills the cavity to seal and protect
the internal electronic circuitry and components. The
front impact sensors are each connected to the vehi-
cle electrical system through a dedicated take out
and connector of the headlamp and dash wire har-
ness.
The impact sensors cannot be repaired or adjusted
and, if damaged or faulty, they must be replaced. The
mounting bracket for the left front impact sensor on
models with a diesel engine is serviced as a unit with
that sensor.
OPERATION
The front impact sensors are electronic accelerom-
eters that sense the rate of vehicle deceleration,
which provides verification of the direction and sever-
ity of an impact. Each sensor also contains an elec-
tronic communication chip that allows the unit to
communicate the sensor status as well as sensor
fault information to the microprocessor in the Airbag
Control Module (ACM). The ACM microprocessor con-
tinuously monitors all of the front passive restraint
system electrical circuits to determine the system
readiness. If the ACM detects a monitored system
fault, it sets a Diagnostic Trouble Code (DTC) and
controls the airbag indicator operation accordingly.
The impact sensors each receive battery current and
ground through dedicated left and right sensor plus and
minus circuits from the ACM. The impact sensors and
the ACM communicate by modulating the voltage in the
sensor plus circuit. The hard wired circuits between the
front impact sensors and the ACM may be diagnosed
and tested using conventional diagnostic tools and pro-
cedures. However, conventional diagnostic methods will
not prove conclusive in the diagnosis of the ACM or the
impact sensors. The most reliable, efficient, and accu-
rate means to diagnose the impact sensors, the ACM,
and the electronic message communication between the
sensors and the ACM requires the use of a DRBIIIt
scan tool. Refer to the appropriate diagnostic informa-
tion.
Fig. 17 Front Impact Sensor
1 - SENSOR
2 - CONNECTOR RECEPTACLE
KJRESTRAINTS 8O - 21