2002 JEEP LIBERTY Turn

FUEL LEVEL SENDING UNIT /
SENSOR
DESCRIPTION
The fuel gauge sending unit (fuel level sensor) is
attached to the side of the fuel pump module. The
sending unit consists of a float, an arm, and a vari-
able resistor track (card).
OPERATION
The fuel pump module has 4 different circuits
(wires). Two of these circuits are used for the fuel
gauge sending unit for fuel gauge operation, and for
certain OBD II emission requirements. The other 2
wires are used for electric fuel pump operation.
For Fuel Gauge Operation:A constant current
source of approximately 32 milliamps is supplied to
the resistor track on the fuel gauge sending unit.
This is fed directly from the Powertrain Control Mod-
ule (PCM).NOTE: For diagnostic purposes, this
12V power source can only be verified with the
circuit opened (fuel pump module electrical
connector unplugged). With the connectors
plugged, output voltages will vary from about
0.6 volts at FULL, to about 8.6 volts at EMPTY
(about 8.6 volts at EMPTY for Jeep models, and
about 7.0 volts at EMPTY for Dodge Truck mod-
els).The resistor track is used to vary the voltage
(resistance) depending on fuel tank float level. As
fuel level increases, the float and arm move up,
which decreases voltage. As fuel level decreases, the
float and arm move down, which increases voltage.
The varied voltage signal is returned back to the
PCM through the sensor return circuit.
Both of the electrical circuits between the fuel
gauge sending unit and the PCM are hard-wired (not
multi-plexed). After the voltage signal is sent from
the resistor track, and back to the PCM, the PCM
will interpret the resistance (voltage) data and send
a message across the multi-plex bus circuits to the
instrument panel cluster. Here it is translated into
the appropriate fuel gauge level reading. Refer to
Instrument Panel for additional information.
For OBD II Emission Monitor Requirements:
The PCM will monitor the voltage output sent from
the resistor track on the sending unit to indicate fuel
level. The purpose of this feature is to prevent the
OBD II system from recording/setting false misfire
and fuel system monitor diagnostic trouble codes.
The feature is activated if the fuel level in the tank
is less than approximately 15 percent of its rated
capacity. If equipped with a Leak Detection Pump
(EVAP system monitor), this feature will also be acti-
vated if the fuel level in the tank is more than
approximately 85 percent of its rated capacity.
DIAGNOSIS AND TESTING - FUEL LEVEL
SENDING UNIT
The fuel level sending unit contains a variable
resistor (track). As the float moves up or down, elec-
trical resistance will change. Refer to Instrument
Panel and Gauges for Fuel Gauge testing. To test the
gauge sending unit only, it must be removed from
vehicle. The unit is a separate part of the lower fuel
pump module section. Refer to Fuel Pump Module
Removal/Installation for procedures (remove only the
upper section of the fuel pump module). Measure the
resistance across the sending unit terminals. With
float in up position, resistance should be 20 ohms (+/-
5%). With float in down position, resistance should be
270 ohms (+/- 5%).
REMOVAL
The fuel level sending unit (fuel level sensor) and
float assembly is located on the side of the lower sec-
tion of the fuel pump module. The lower section of
the fuel pump module is located within the fuel tank.
(1) Remove lower section of fuel pump module
from fuel tank. Refer to Fuel Pump Module Removal/
Installation.
(2) To remove sending unit from pump module, lift
on plastic locking tab (Fig. 8) while sliding sending
unit upwards.
(3) Disconnect 4±wire electrical connector (Fig. 9)
from bottom of upper section of fuel pump module.
Separate necessary sending unit wiring.
Fig. 8 FUEL LEVEL SENDING UNIT
1 - LIFT TAB HERE FOR REMOVAL
2 - FUEL LEVEL SENDING UNIT
3 - LOWER SECTION OF PUMP MODULE
KJFUEL DELIVERY 14 - 9

OPERATION
The fuel pressure regulator is a mechanical device
that is not controlled by engine vacuum or the Pow-
ertrain Control Module (PCM).
The regulator is calibrated to maintain fuel system
operating pressure of approximately 339 kPa +/- 34
kPa (49.2 psi +/- 5 psi) at the fuel injectors. It con-
tains a diaphragm, calibrated springs and a fuel
return valve.
The main fuel filteris not combinedwithin the
fuel pressure regulator as in other Jeeptmodels.
Three different fuel filters are used: 1. a serviceable,
separate, externally mounted, main fuel filter; 2. a
non-serviceable primary filter located on the bottom
of the electric fuel pump; 3. a non-serviceable second-
ary filter attached to the side of the fuel pump mod-
ule.
Fuel Flow:Fuel migrates into the fuel pump mod-
ule reservoir through a one-way check valve located
on the bottom of the module. This check valve pre-
vents the reservoir from running empty such as
when going up or down hills with a low amount of
fuel in the tank. A primary fuel filter (sock) is located
at the bottom of the electric fuel pump. Fuel is drawn
in through this filter, and up to the electric fuel
pump. High pressure fuel (unregulated) is supplied
from the electric fuel pump through a high-pressure
line to one of 3 fittings on the main fuel filter. If fuel
pressure at the pressure regulator exceeds approxi-
mately 49 psi, an internal diaphragm within the reg-
ulator closes, and excess fuel is routed through a
second fitting on the main fuel filter, and back into
the fuel tank (the fuel pressure regulator is installed
into the return side of the system). Pressure regu-
lated fuel is then delivered from the third fitting on
the fuel filter, up to and through the fuel rail, and on
to the fuel injectors.
A secondary fuel filter is attached to the side of the
fuel pump module. High-pressure from the electric
fuel pump causes a siphoning action across a passage
connected to this filter, and fuel is drawn into the
fuel pump module reservoir. This is used to help keep
the module reservoir full of fuel.
The fuel pressure regulator also acts as a check
valve to maintain some fuel pressure when the
engine is not operating. This will help to start the
engine. A second check valve is located at the outlet
of the fuel pump module housing.Refer to Fuel
Pump - Description and Operation for more
information. Also refer to the Fuel Pressure
Leak Down Test, and the Fuel Pump Pressure
Tests.
A separate fuel return line from the engine is not
used with this system.
REMOVAL
The fuel pressure regulator is located in the fuel
tank. It is attached to the bottom of the upper sec-
tion of the fuel pump module with a quick-connect
fitting (Fig. 19). The fuel pump module is supplied in
2 sections (upper and lower). To replace the pressure
regulator, the bottom section of the fuel pump mod-
ule must be replaced.
(1) Remove upper and lower sections of fuel pump
module from fuel tank. Refer to Fuel Pump Module
Removal/Installation.
(2) Replace lower section of fuel pump module
(includes fuel pressure regulator).
INSTALLATION
The fuel pressure regulator is located in the fuel
tank. It is attached to the bottom of the upper sec-
tion of the fuel pump module with a quick-connect
fitting. The fuel pump module is supplied in 2 sec-
tions (upper and lower). To replace the pressure reg-
ulator, the bottom section of the fuel pump module
must be replaced.
(1) Replace lower section of fuel pump module
(includes fuel pressure regulator).
(2) Install upper and lower sections of fuel pump
module to fuel tank. Refer to Fuel Pump Module
Installation.
Fig. 19 FUEL PRESSURE REGULATOR/SENDING
UNIT ELECTRICAL CONNECTOR
1 - UPPER SECTION OF PUMP MODULE
2 - QUICK-CONNECT FITTINGS
3 - FUEL PRESSURE REGULATOR
4 - 4-WIRE ELECTRICAL CONNECTOR
5 - FUEL TANK CHECK (CONTROL) VALVE
14 - 14 FUEL DELIVERYKJ
FUEL PRESSURE REGULATOR (Continued)

(17) When LCS adapter test leads are attached
into relay cavities, fuel pumpwill be activated.
Determine fuel pump amperage on DRB screen.
Amperage should be below 10.0 amps. If amperage is
below 10.0 amps, and specifications for the Fuel
Pump Pressure, Fuel Pump Capacity and Fuel Pres-
sure Leak Down tests were met, the fuel pump mod-
ule is OK.
(18) If amperage is more than 10.0 amps, replace
fuel pump module assembly. The electric fuel pump
is not serviced separately.
(19) Disconnect test leads from relay cavities
immediately after testing.
FUEL PUMP MODULE
DESCRIPTION
The fuel pump module assembly is located in the
fuel tank (Fig. 1). The assembly is divided into 2±sec-
tions, upper and lower. The lower section is locked to
the bottom of the fuel tank. The complete assembly
contains the following components:
²A fuel pressure regulator
²A separate fuel pick-up, or inlet filter
²An electric fuel pump
²A lockring to retain upper section of pump mod-
ule to tank
²A rollover valve
²A vent fitting for ORVR system
²A soft gasket between tank flange and module
²A fuel gauge sending unit (fuel level sensor)
²Two fuel line connections (supply and return)
The fuel gauge sending unit may be serviced sepa-
rately. If the electrical fuel pump, primary inlet filter
or fuel pressure regulator require service, the lower
section of the fuel pump module must be replaced.
OPERATION
Refer to Fuel Pump, Inlet Filter, Fuel Pressure
Regulator and Fuel Gauge Sending Unit.
REMOVAL
The fuel pump module is divided into 2 sections,
upper and lower. To service the check (control) valve,
replace only the upper section. To service the fuel
gauge sending unit, remove the upper section. To ser-
vice the electric fuel pump, fuel pressure regulator or
primary inlet filter, remove both sections and replace
lower section.
Fuel tank removal will not be necessary for
fuel pump module removal. Access is from rear
cargo area.
(1) Four cargo holdown clamps are located inside
the vehicle on the floor of the rear cargo area.Remove the 2 rearward mounted clamps by drilling
out the clamp rivets.
(2) Fold carpeting forward to gain access to fuel
pump module access plate (Fig. 25).
(3) Remove 4 fuel pump module access plate nuts
(Fig. 25).
(4) While applying heat from a heat gun, carefully
pry up fuel pump module access plate. Take care not
to bend plate.
(5) Thoroughly clean area around top of pump
module to prevent contaminants from entering fuel
tank or fuel lines.
WARNING: THE FUEL SYSTEM IS UNDER A CON-
STANT PRESSURE EVEN WITH ENGINE OFF.
BEFORE SERVICING THE FUEL PUMP MODULE,
FUEL SYSTEM PRESSURE MUST BE RELEASED.
(6) Release fuel system pressure. Refer to Fuel
System Pressure Release procedure.
(7) Disconnect 2 fuel lines at fuel pump module
(Fig. 26) by pressing on 2 buttons at sides of fitting.
(8) Disconnect electrical connector (Fig. 26) at top
of fuel pump module by sliding red colored tab first
to unlock, and push grey colored tab down for
removal.
(9) Disconnect ORVR hose clamp and hose (Fig.
26) at pump module fitting.
(10) Remove module lockring (Fig. 26) using a
brass drift and hammer (counter-clockwise).
(11) Carefully lift upper section of pump module
(Fig. 26) from fuel tank exposing connections(lift
upper section from tank very slowly until rub-
ber gasket can be retained. If not, gasket will
fall into fuel tank.)
(a) Disconnect electrical connector (Fig. 27) at
bottom of upper pump module section.
(b) Disconnect fuel pressure regulator (Fig. 27)
at bottom of upper pump module section. Press on
2 locking tabs.
(c) Disconnect fuel return line (Fig. 27) at bot-
tom of upper pump module section. Press on 2
locking tabs.
(d) Remove upper section of pump module (Fig.
28) from fuel tank.
(12) Using an approved gas holding tank, drain
fuel tank through pump module opening.If check
(control) valve, or, only upper section of pump
module is being serviced, tank draining is not
necessary. If any other fuel pump module com-
ponent is being serviced, the tank must be com-
pletely drained to the bottom.
(13) To remove lower section of pump module from
fuel tank:
(a) Using finger pressure, push on plastic
release tab (Fig. 29) while sliding lock tab upward.
14 - 18 FUEL DELIVERYKJ
FUEL PUMP (Continued)

of the firing of the fuel injectors. It isnot usedas a
fuel pressure regulator. The fuel pressure regulator is
not mountedto the fuel rail on any engine. It is
located on the fuel tank mounted fuel pump module.
Refer to Fuel Pressure Regulator for additional infor-
mation.
The fuel rail is not repairable.
A quick-connect fitting with a safety latch is used
to attach the fuel line to the fuel rail.
3.7L
High pressure fuel from the fuel pump is routed to
the fuel rail. The fuel rail then supplies the neces-
sary fuel to each individual fuel injector.
A quick-connect fitting with a safety latch is used
to attach the fuel line to the fuel rail.
The fuel rail is not repairable.
REMOVAL
2.4L
WARNING: THE FUEL SYSTEM IS UNDER CON-
STANT PRESSURE EVEN WITH ENGINE OFF.
BEFORE SERVICING FUEL RAIL, FUEL SYSTEM
PRESSURE MUST BE RELEASED.
The fuel rail can be removed without removing the
intake manifold if the following procedures are fol-
lowed.(1) Remove fuel tank filler tube cap.
(2) Perform Fuel System Pressure Release Proce-
dure.
(3) Remove negative battery cable at battery.
(4) Remove air duct at throttle body.
(5) Disconnect fuel line latch clip and fuel line at
fuel rail. A special tool will be necessary for fuel line
disconnection. Refer to Quick-Connect Fittings.
(6) Remove necessary vacuum lines at throttle
body.
(7) Drain engine coolant and remove thermostat
and thermostat housing.
(8) Remove PCV hose and valve at valve cover.
(9) Remove 3 upper intake manifold mounting
bolts (Fig. 35), but only loosen 2 lower bolts about 2
turns.
(10) Disconnect 2 main engine harness connectors
at rear of intake manifold (Fig. 34).
(11) Disconnect 2 injection wiring harness clips at
harness mounting bracket (Fig. 35).
(12) Disconnect electrical connectors at all 4 fuel
injectors. To remove connector refer to (Fig. 37). Push
red colored slider away from injector (1). While push-
ing slider, depress tab (2) and remove connector (3)
from injector. The factory fuel injection wiring har-
ness is numerically tagged (INJ 1, INJ 2, etc.) for
injector position identification. If harness is not
tagged, note wiring location before removal.
(13) Remove 2 injection rail mounting bolts (Fig.
31).
Fig. 34 MAP SENSOR LOCATION-2.4L
1 - REAR OF INTAKE MANIFOLD
2 - MAP SENSOR
3 - ALIGNMENT PIN
4 - MOUNTING BOLT (TORX)
5 - ELECTRICAL CONNECTOR
6 - MAIN ENGINE HARNESS CONNECTORS
Fig. 35 FUEL RAIL MOUNTING-2.4L
1 - FUEL RAIL
2 - INJECTION HARNESS CLIPS
3 - LOWER MOUNTING HOLES
4 - UPPER MOUNTING HOLES
5 - INTAKE MANIFOLD
14 - 22 FUEL DELIVERYKJ
FUEL RAIL (Continued)

REMOVAL
(1) Remove fuel rail. Refer to Fuel Injector Rail
Removal.
(2) Disconnect clip(s) that retain fuel injector(s) to
fuel rail (Fig. 10).
INSTALLATION
(1) Install fuel injector(s) into fuel rail assembly
and install retaining clip(s).
(2) If same injector(s) is being reinstalled, install
new o-ring(s).
(3) Apply a small amount of clean engine oil to
each injector o-ring. This will aid in installation.
(4) Install fuel rail. Refer to Fuel Rail Installation.
(5) Start engine and check for fuel leaks.
FUEL PUMP RELAY
DESCRIPTION
The 5±pin, 12±volt, fuel pump relay is located in
the Power Distribution Center (PDC). Refer to the
label on the PDC cover for relay location.
OPERATION
The Powertrain Control Module (PCM) energizes
the electric fuel pump through the fuel pump relay.
The fuel pump relay is energized by first applying
battery voltage to it when the ignition key is turnedON, and then applying a ground signal to the relay
from the PCM.
Whenever the ignition key is turned ON, the elec-
tric fuel pump will operate. But, the PCM will shut-
down the ground circuit to the fuel pump relay in
approximately 1±3 seconds unless the engine is oper-
ating or the starter motor is engaged.
DIAGNOSIS AND TESTING - FUEL PUMP
RELAY
For procedures, refer to ASD Relay Diagnosis and
Testing in the Ignition section.
REMOVAL
The fuel pump relay is located in the Power Distri-
bution Center (PDC) (Fig. 11). Refer to label on PDC
cover for relay location.
(1) Remove PDC cover.
(2) Remove relay from PDC.
(3) Check condition of relay terminals and PDC
connector terminals for damage or corrosion. Repair
if necessary before installing relay.
(4) Check for pin height (pin height should be the
same for all terminals within the PDC connector).
Repair if necessary before installing relay.
INSTALLATION
The fuel pump relay is located in the Power Distri-
bution Center (PDC). Refer to label on PDC cover for
relay location.
(1) Install relay to PDC.
(2) Install cover to PDC.
Fig. 10 INJECTOR RETAINING CLIP
1 - PLIERS
2 - INJECTOR CLIP
3 - FUEL INJECTOR
4 - FUEL RAIL - TYPICAL
Fig. 11 POWER DISTRIBUTION CENTER (PDC)
1 - BATTERY
2 - PDC
3 - PDC COVER
14 - 34 FUEL INJECTIONKJ
FUEL INJECTOR (Continued)

REMOVAL
2.4L
The Idle Air Control (IAC) motor is located on the
rear side of the throttle body (Fig. 12).
(1) Disconnect electrical connector from IAC motor.
(2) Remove two mounting bolts (screws).
(3) Remove IAC motor from throttle body.
3.7L
The Idle Air Control (IAC) motor is located on the
side of the throttle body (Fig. 13).
(1) Disconnect electrical connector from IAC motor.
(2) Remove two mounting bolts (screws).
(3) Remove IAC motor from throttle body.
INSTALLATION
2.4L
The Idle Air Control (IAC) motor is located on the
rear side of the throttle body.
(1) Install IAC motor to throttle body.
(2) Install and tighten two mounting bolts (screws)
to 7 N´m (60 in. lbs.) torque.
(3) Install electrical connector.
3.7L
The Idle Air Control (IAC) motor is located on the
side of the throttle body (Fig. 13).
(1) Install IAC motor to throttle body.(2) Install and tighten two mounting bolts (screws)
to 7 N´m (60 in. lbs.) torque.
(3) Install electrical connector.
INTAKE AIR TEMPERATURE
SENSOR
DESCRIPTION
The 2±wire Intake Manifold Air Temperature (IAT)
sensor is installed in the intake manifold with the
sensor element extending into the air stream.
The IAT sensor is a two-wire Negative Thermal
Coefficient (NTC) sensor. Meaning, as intake mani-
fold temperature increases, resistance (voltage) in the
sensor decreases. As temperature decreases, resis-
tance (voltage) in the sensor increases.
OPERATION
The IAT sensor provides an input voltage to the
Powertrain Control Module (PCM) indicating the
density of the air entering the intake manifold based
upon intake manifold temperature. At key-on, a
5±volt power circuit is supplied to the sensor from
the PCM. The sensor is grounded at the PCM
through a low-noise, sensor-return circuit.
The PCM uses this input to calculate the following:
²Injector pulse-width
²Adjustment of spark timing (to help prevent
spark knock with high intake manifold air-charge
temperatures)
Fig. 12 TPS/IAC MOTOR - 2.4L
1 - THROTTLE POSITION SENSOR (TPS)
2 - MOUNTING SCREWS
3 - IDLE AIR CONTROL MOTOR (IAC)
4 - MOUNTING SCREWS
Fig. 13 TPS/IAC MOTOR - 3.7L
1 - THROTTLE POSITION SENSOR (TPS)
2 - MOUNTING SCREWS
3 - IDLE AIR CONTROL MOTOR (IAC)
4 - MOUNTING SCREWS
14 - 36 FUEL INJECTIONKJ
IDLE AIR CONTROL MOTOR (Continued)

The resistance values of the IAT sensor is the same
as for the Engine Coolant Temperature (ECT) sensor.
REMOVAL
2.4L
The intake manifold air temperature (IAT) sensor
is installed into the intake manifold plenum at the
rear end of the intake manifold (Fig. 14).
(1) Disconnect electrical connector from IAT sen-
sor.
(2) Clean dirt from intake manifold at sensor base.
(3) Gently lift on small plastic release tab (Fig. 14)
or (Fig. 15) and rotate sensor about 1/4 turn counter-
clockwise for removal.
(4) Check condition of sensor o-ring (Fig. 15).
3.7L
The intake manifold air temperature (IAT) sensor
is installed into the left side of intake manifold ple-
num (Fig. 16).
(1) Disconnect electrical connector from IAT sen-
sor.
(2) Clean dirt from intake manifold at sensor base.
(3) Gently lift on small plastic release tab (Fig. 16)
or (Fig. 15) and rotate sensor about 1/4 turn counter-
clockwise for removal.
(4) Check condition of sensor o-ring.
Fig. 14 IAT SENSOR LOCATION-2.4L
1 - RELEASE TAB
2 - IAT SENSOR
3 - PRESS HERE FOR REMOVAL
4 - ELECTRICAL CONNECTOR
5 - REAR END OF INTAKE MANIFOLD
Fig. 15 IAT SENSOR TAB / O-RING
1 - IAT SENSOR
2 - SENSOR O-RING
3 - RELEASE TAB
Fig. 16 IAT SENSOR LOCATION- 3.7L
1 - IAT SENSOR
2 - RELEASE TAB
3 - ELECTRICAL CONNECTOR
KJFUEL INJECTION 14 - 37
INTAKE AIR TEMPERATURE SENSOR (Continued)

INSTALLATION
2.4L
The intake manifold air temperature (IAT) sensor
is installed into the intake manifold plenum at the
rear end of the intake manifold.
(1) Check condition of sensor o-ring.
(2) Clean sensor mounting hole in intake manifold.
(3) Position sensor into intake manifold and rotate
clockwise until past release tab.
(4) Install electrical connector.
3.7L
The intake manifold air temperature (IAT) sensor
is installed into the left side of intake manifold ple-
num (Fig. 16).
(1) Check condition of sensor o-ring.
(2) Clean sensor mounting hole in intake manifold.
(3) Position sensor into intake manifold and rotate
clockwise until past release tab (Fig. 16).
(4) Install electrical connector.
MAP SENSOR
DESCRIPTION
2.4L
The Manifold Absolute Pressure (MAP) sensor is
mounted into the rear of the intake manifold with 1
screw.
3.7L
The Manifold Absolute Pressure (MAP) sensor is
mounted into the front of the intake manifold with 2
screws.
OPERATION
The MAP sensor is used as an input to the Power-
train Control Module (PCM). It contains a silicon
based sensing unit to provide data on the manifold
vacuum that draws the air/fuel mixture into the com-
bustion chamber. The PCM requires this information
to determine injector pulse width and spark advance.
When manifold absolute pressure (MAP) equals
Barometric pressure, the pulse width will be at max-
imum.
A 5 volt reference is supplied from the PCM and
returns a voltage signal to the PCM that reflects
manifold pressure. The zero pressure reading is 0.5V
and full scale is 4.5V. For a pressure swing of 0±15
psi, the voltage changes 4.0V. To operate the sensor,
it is supplied a regulated 4.8 to 5.1 volts. Ground is
provided through the low-noise, sensor return circuit
at the PCM.The MAP sensor input is the number one contrib-
utor to fuel injector pulse width. The most important
function of the MAP sensor is to determine baromet-
ric pressure. The PCM needs to know if the vehicle is
at sea level or at a higher altitude, because the air
density changes with altitude. It will also help to cor-
rect for varying barometric pressure. Barometric
pressure and altitude have a direct inverse correla-
tion; as altitude goes up, barometric goes down. At
key-on, the PCM powers up and looks at MAP volt-
age, and based upon the voltage it sees, it knows the
current barometric pressure (relative to altitude).
Once the engine starts, the PCM looks at the voltage
again, continuously every 12 milliseconds, and com-
pares the current voltage to what it was at key-on.
The difference between current voltage and what it
was at key-on, is manifold vacuum.
During key-on (engine not running) the sensor
reads (updates) barometric pressure. A normal range
can be obtained by monitoring a known good sensor.
As the altitude increases, the air becomes thinner
(less oxygen). If a vehicle is started and driven to a
very different altitude than where it was at key-on,
the barometric pressure needs to be updated. Any
time the PCM sees Wide Open Throttle (WOT), based
upon Throttle Position Sensor (TPS) angle and RPM,
it will update barometric pressure in the MAP mem-
ory cell. With periodic updates, the PCM can make
its calculations more effectively.
The PCM uses the MAP sensor input to aid in cal-
culating the following:
²Manifold pressure
²Barometric pressure
²Engine load
²Injector pulse-width
²Spark-advance programs
²Shift-point strategies (certain automatic trans-
missions only)
²Idle speed
²Decel fuel shutoff
The MAP sensor signal is provided from a single
piezoresistive element located in the center of a dia-
phragm. The element and diaphragm are both made
of silicone. As manifold pressure changes, the dia-
phragm moves causing the element to deflect, which
stresses the silicone. When silicone is exposed to
stress, its resistance changes. As manifold vacuum
increases, the MAP sensor input voltage decreases
proportionally. The sensor also contains electronics
that condition the signal and provide temperature
compensation.
The PCM recognizes a decrease in manifold pres-
sure by monitoring a decrease in voltage from the
reading stored in the barometric pressure memory
cell. The MAP sensor is a linear sensor; meaning as
pressure changes, voltage changes proportionately.
14 - 38 FUEL INJECTIONKJ
INTAKE AIR TEMPERATURE SENSOR (Continued)