Turn signal DODGE RAM 1500 1998 2.G Owners Manual

TAIL/STOP/TURN SIGNAL LAMP-LEFT-6WAY
CAV CIRCUIT FUNCTION
1 L7 18WT/YL FUSED PARK LAMP RELAY OUTPUT
2- -
3 Z928 18BK GROUND
4 L53 18DG/WT LEFT STOP LAMP FEED
5 L63 18WT/DG LEFT REAR TURN LAMP DRIVER
6 L1 18WT/LG BACKUP LAMP FEED
TAIL/STOP/TURN SIGNAL LAMP-RIGHT - BLACK 6 WAY
CAV CIRCUIT FUNCTION
1 L70 18WT/GY FUSED PARK LAMP RELAY OUTPUT
1 L70 18WT/YL FUSED PARK LAMP RELAY OUTPUT
2- -
3 Z928 18BK GROUND
4 L54 18DG/WT RIGHT STOP LAMP FEED
4 L54 18WT/LG RIGHT STOP LAMP FEED
5 L62 18WT/YL RIGHT REAR TURN LAMP DRIVER
5 L62 18WT/DG RIGHT REAR TURN LAMP DRIVER
6 L1 18WT/LG BACKUP LAMP FEED
TAILGATE LAMP-2WAY
CAV CIRCUIT FUNCTION
1 L7 18WT/YL FUSED PARK LAMP RELAY OUTPUT
2 Z942 20BK GROUND
THROTTLE POSITION SENSOR (3.7L)-3WAY
CAV CIRCUIT FUNCTION
1 F855 18PK/YL 5 VOLT SUPPLY
2 K900 18DB/DG SENSOR GROUND
3 K22 18BR/OR TP NO. 1 SIGNAL
8W - 80 - 98 8W-80 CONNECTOR PIN-OUTSDR

THROTTLE POSITION SENSOR (4.7L)-3WAY
CAV CIRCUIT FUNCTION
1 F855 18PK/YL 5 VOLT SUPPLY
2 K22 18BR/OR TP NO. 1 SIGNAL
3 K900 18DB/DG SENSOR GROUND
TOW/HAUL OVERDRIVE SWITCH - WHITE 2 WAY
CAV CIRCUIT FUNCTION
1 T6 20DG TOW/HAUL OVERDRIVE OFF SWITCH SENSE
2 Z71 20LB/BK GROUND
TRAILER TOW CONNECTOR-4WAY
CAV CIRCUIT FUNCTION
1 Z999 14BK GROUND
2 L678 18BR PARK LAMP RELAY OUTPUT
3 L673 18YL TRAILER TOW LEFT TURN RELAY OUTPUT
4 L674 18LG TRAILER TOW RIGHT TURN RELAY OUTPUT
TRAILER TOW CONNECTOR-ADD ON - 10 WAY
CAV CIRCUIT FUNCTION
1- -
2 L674 18LG TRAILER TOW RIGHT TURN RELAY OUTPUT
3 L1 18WT/LG BACKUP LAMP FEED
4 A100 14RD/VT FUSED B(+)
5 L678 18BR PARK LAMP RELAY OUTPUT
6- -
7 B40 14DG TRAILER TOW BRAKE B(+)
8 Z999 14BK GROUND
9 Z999 14BK GROUND
10 L673 18YL TRAILER TOW LEFT TURN RELAY OUTPUT
DR8W-80 CONNECTOR PIN-OUTS 8W - 80 - 99

CONNECTOR NAME/NUMBER COLOR LOCATION FIG.
Mode Door Actuator 2 BK Right Side of HVAC N/S
Multi-Function Switch BK On Steering Column 31
Natural Vacuum Leak Detection
AssemblyBK Rear of Transmission 18, 50
Output Speed Sensor DB Left Side of Transmission 11, 14, 15, 16
Overdrive Switch WT Center of Instrument Panel 35
Overhead Map/Reading Lamp
(Except Base)NAT Center of Headliner N/S
Oxygen Sensor 1/1 Upstream BK Left Front of Side of Transmission 15, 16, 17, 19
Oxygen Sensor 1/2 Downstream NAT Left Rear of Side of Transmission 15, 16, 17, 19
Oxygen Sensor 2/1 Upstream BK Right Front Side of Transmission 15, 17, 18
Oxygen Sensor 2/2 Downstream BK Right Rear Side of Transmission 15, 17, 18
Park Brake Switch At Park Brake 22, 24
Park/Turn Signal Lamp-Left Front BK At Lamp 23, 28, 29
Park/Turn Signal Lamp-Right Front BK At Lamp 1, 21, 26
Passenger Airbag On/Off Switch Right Side of Instrument Panel 33, 35, 39
Passenger Blend Door Actuator
(Dual Zone)BK Right Side of HVAC N/S
Passenger Lumbar Switch At Passenger Seat N/S
Power Mirror-Left BK At Mirror 41
Power Mirror-Right BK At Mirror 42
Power Outlet RD Center of Instrument Panel 35
Power Outlet-Console BK Center of Instrument Panel N/S
Power Seat Motor-Driver Front
VerticalRD At Driver Seat N/S
Power Seat Motor-Driver Horizontal BK At Driver Seat N/S
Power Seat Motor-Driver Rear
VerticalBK At Driver Seat N/S
Power Seat Switch-Driver BK At Driver Seat N/S
Power Seat Switch-Passenger BK At Passenger Seat N/S
Power Steering Pressure Switch BK Near Power Steering Pump 7
Power Window Circuit Breaker Under Instrument Panel 31, 35, 38
Power Window Motor-Driver BK In Driver Door at Motor 41
Power Window Motor-Left Rear BK In Door at Motor 43
Power Window Motor-Passenger BK In Passenger Door at Motor 42
Power Window Motor-Right Rear BK In Door at Motor 43
Power Window Switch-Left Rear BL In Door 43
Power Window Switch-Passenger Passenger Door 42
Power Window Switch-Right Rear BL In Door 43
Powertrain Control Module C1 BK Right Rear Engine Compartment 4, 8
Powertrain Control Module C2 WT Right Rear Engine Compartment 4, 8
Powertrain Control Module C3 GY Right Rear Engine Compartment 21
Powertrain Control Module C4 GN Right Rear Engine Compartment 4, 8
8W - 91 - 6 8W-91 CONNECTOR/GROUND/SPLICE LOCATIONDR
CONNECTOR/GROUND/SPLICE LOCATION (Continued)

CONNECTOR NAME/NUMBER COLOR LOCATION FIG.
Speed Control Switch-Right (ETC) WT At Steering Wheel N/S
Starter Solenoid Left Engine 23
Tail/Stop/Turn Signal Lamp-Left BK At Lamp 50, 51
Tail/Stop/Turn Signal Lamp-Right BK At Lamp 50, 51
Throttle Position Sensor NAT Throttle Body 6
Trailer Tow Connector BK At Trailer Hitch 51
Trailer Tow Connector-Add On BK At Trailer Hitch 51, 53
Transfer Case Control Module C1 BK Left Side of Instrument Panel 35, 38
Transfer Case Control Module C2 GY Left Side of Instrument Panel 35, 38
Transfer Case Control Module C3 BK Left Side of Instrument Panel 35, 38
Transfer Case Mode Sensor BK Left Front Side of Transfer Case 13, 14, 16, 20
Transfer Case Position Sensor BK Front Middle of Transfer Case 20
Transfer Case Selector Switch BK Center of Instrument Panel 11, 12, 33, 35, 36
Transfer Case Shift Motor BK Left Rear of Transmission 13, 14, 20
Transmission Range Sensor BK Left side of Transmission 11, 14
Transmission Solenoid Assembly BK Left Side of Transmission 14, 11
Transmission Solenoid/TRS
Assembly (3.7L/4.7L)BK Left Side of Transmission 15, 16
Underhood Lamp BK Underside of Hood 29
Vacuum Pump (Diesel) Right Rear Engine Compartment 21
Vistronic Fan Drive Front Engine Compartment 28
Washer Fluid Level Switch BK At Reservoir 21, 23, 26, 28
Washer Pump Motor-Front BK At Washer Fluid Reservoir 21, 23, 26, 28
Water In Fuel Sensor (Diesel) BK Right Side Engine 10
Wheel Speed Sensor-Left Front BK Left Rear Lower Side of Engine
Compartment22, 29
Wheel Speed Sensor-Rear BK Right Rear of Body 51
Wheel Speed Sensor-Right Front GY Right Rear Lower Side of Engine
Compartment21
Wiper Motor-Front BK Left Side of Cowl 22, 25
8W - 91 - 8 8W-91 CONNECTOR/GROUND/SPLICE LOCATIONDR
CONNECTOR/GROUND/SPLICE LOCATION (Continued)

(12) Install the front crossmember(Refer to 13 -
FRAME & BUMPERS/FRAME/FRONT CROSS-
MEMBER - INSTALLATION).
(13) Fill engine oil.
(14) Reconnect the negative battery cable.
(15) Start engine and check for leaks.
OIL PRESSURE SENSOR/
SWITCH
DESCRIPTION
The 3 wire, solid-state engine oil pressure sensor
(sending unit) is located in an engine oil pressure
gallery.
OPERATION
The oil pressure sensor uses three circuits. They
are:
²A 5 volt power supply from the Powertrain Con-
trol Module (PCM)
²A sensor ground through the PCM's sensor
return
²A signal to the PCM relating to engine oil pres-
sure
The oil pressure sensor has a 3 wire electrical
function very much like the Manifold Absolute Pres-
sure (MAP) sensor. Meaning different pressures
relate to different output voltages.
A 5 volt supply is sent to the sensor from the PCM
to power up the sensor. The sensor returns a voltage
signal back to the PCM relating to engine oil pres-
sure. This signal is then transferred (bussed) to theinstrument panel on either a CCD or PCI bus circuit
(depending on vehicle line) to operate the oil pressure
gauge and the check gauges lamp. Ground for the
sensor is provided by the PCM through a low-noise
sensor return.
REMOVAL
(1) Disconnect the negative cable from the battery.
(2) Raise vehicle on hoist.
(3) Remove front splash shield.
(4) Disconnect oil pressure sender wire (Fig. 75).
(5) Remove the pressure sender (Fig. 75).
INSTALLATION
(1) Install oil pressure sender.
(2) Connect oil pressure sender wire.
(3) Install front splash shield.
(4) Lower vehicle.
(5) Connect the negative battery cable.
OIL PUMP
REMOVAL
(1) Remove the oil pan and pick-up tube (Refer to
9 - ENGINE/LUBRICATION/OIL PAN - REMOVAL).
(2) Remove the timing chain cover (Refer to 9 -
ENGINE/VALVE TIMING/TIMING BELT / CHAIN
COVER(S) - REMOVAL).
Fig. 74 Oil Pan Mounting Bolt Sequence
Fig. 75 OIL PRESSURE SENDING UNIT
1 - BELT
2 - OIL PRESSURE SENSOR
3 - OIL FILTER
4 - ELEC. CONNECTOR
DRENGINE - 3.7L 9 - 67
OIL PAN (Continued)

OIL PRESSURE SENSOR/
SWITCH
DESCRIPTION
DESCRIPTION
The 3 wire, solid-state engine oil pressure sensor
(sending unit) is located in an engine oil pressure
gallery.
DESCRIPTION
The 3±wire, electrical/mechanical engine oil pres-
sure sensor (sending unit) is located in an engine oil
pressure gallery.
OPERATION
OPERATION
The oil pressure sensor uses three circuits. They
are:
²A 5 volt power supply from the Powertrain Con-
trol Module (PCM)
²A sensor ground through the PCM's sensor
return
²A signal to the PCM relating to engine oil pres-
sure
The oil pressure sensor has a 3 wire electrical
function very much like the Manifold Absolute Pres-
sure (MAP) sensor. Meaning different pressures
relate to different output voltages.
A 5 volt supply is sent to the sensor from the PCM
to power up the sensor. The sensor returns a voltage
signal back to the PCM relating to engine oil pres-
sure. This signal is then transferred (bussed) to the
instrument panel on either a CCD or PCI bus circuit
(depending on vehicle line) to operate the oil pressure
gauge and the check gauges lamp. Ground for the
sensor is provided by the PCM through a low-noise
sensor return.
OPERATION
The oil pressure sensor uses two circuits. They are:
²A signal to the PCM relating to engine oil pres-
sure
²A sensor ground through the PCM's sensor
return
The oil pressure sensor returns a voltage signal
back to the PCM relating to engine oil pressure. This
signal is then transferred (bussed) to the instrument
panel on a CCD bus circuit to operate the oil pres-
sure gauge and the check gauges lamp. Ground for
the sensor is provided by the PCM through a low-
noise sensor return.
REMOVAL
(1) Disconnect the negative cable from the battery.
(2) Raise vehicle on hoist.
(3) Remove front splash shield.
(4) Disconnect oil pressure sender wire (Fig. 100).
(5) Remove the pressure sender (Fig. 100).
INSTALLATION
(1) Install oil pressure sender.
(2) Connect oil pressure sender wire.
(3) Install front splash shield.
(4) Lower vehicle.
(5) Connect the negative battery cable.
OIL PUMP
REMOVAL
(1) Remove the oil pan and pick-up tube (Refer to
9 - ENGINE/LUBRICATION/OIL PAN - REMOVAL).
(2) Remove the timing chain cover (Refer to 9 -
ENGINE/VALVE TIMING/TIMING BELT / CHAIN
COVER(S) - REMOVAL).
(3) Remove the timing chains and tensioners
(Refer to 9 - ENGINE/VALVE TIMING/TIMING
BELT/CHAIN AND SPROCKETS - REMOVAL).
(4) Remove the four bolts, primary timing chain
tensioner and the oil pump.
Fig. 100 OIL PRESSURE SENDING UNIT
1 - BELT
2 - OIL PRESSURE SENSOR
3 - OIL FILTER
4 - ELEC. CONNECTOR
9 - 156 ENGINE - 4.7LDR

OPERATION
Exhaust gas pressure and energy drive the tur-
bine, which in turn drives a centrifugal compressor
that compresses the inlet air, and forces the air into
the engine through the charge air cooler and plumb-
ing. Since heat is a by-product of this compression,
the air must pass through a charge air cooler to cool
the incoming air and maintain power and efficiency.
Increasing air flow to the engine provides:
²Improved engine performance
²Lower exhaust smoke density
²Improved operating economy
²Altitude compensation
²Noise reduction.
The turbocharger also uses a wastegate (Fig. 16),
which regulates intake manifold air pressure and
prevents over boosting at high engine speeds. When
the wastegate valve is closed, all of the exhaust gases
flow through the turbine wheel. As the intake mani-
fold pressure increases, the wastegate actuator opens
the valve, diverting some of the exhaust gases away
from the turbine wheel. This limits turbine shaft
speed and air output from the impeller.
The turbocharger is lubricated by engine oil that is
pressurized, cooled, and filtered. The oil is delivered
to the turbocharger by a supply line that is tapped
into the oil filter head. The oil travels into the bear-
ing housing, where it lubricates the shaft and bear-
ings (Fig. 17). A return pipe at the bottom of the
bearing housing, routes the engine oil back to the
crankcase.
The most common turbocharger failure is bearing
failure related to repeated hot shutdowns with inad-
equate ªcool-downº periods. A sudden engine shut
down after prolonged operation will result in the
transfer of heat from the turbine section of the tur-
bocharger to the bearing housing. This causes the oil
to overheat and break down, which causes bearing
and shaft damage the next time the vehicle is
started.
Letting the engine idle after extended operation
allows the turbine housing to cool to normal operat-
ing temperature. The following chart should be used
as a guide in determining the amount of engine idle
time required to sufficiently cool down the turbo-
charger before shut down, depending upon the type
of driving and the amount of cargo.
Fig. 16 Wastegate Operation
1 - SIGNAL LINE
2 - EXHAUST BYPASS VALVE
3 - WASTEGATE
4 - EXHAUST
5 - TURBINE
DREXHAUST SYSTEM 11 - 13
TURBOCHARGER (Continued)

OPERATION
Fuel Pressure Regulator Operation:The pres-
sure regulator is a mechanical device that is not con-
trolled by engine vacuum or the Powertrain Control
Module (PCM).
The regulator is calibrated to maintain fuel system
operating pressure of approximately 58   2 psi at the
fuel injectors. It contains a diaphragm, calibrated
springs and a fuel return valve. The internal fuel fil-
ter (Fig. 2) is also part of the assembly.
Fuel is supplied to the filter/regulator by the elec-
tric fuel pump through an opening tube at the bot-
tom of filter/regulator (Fig. 2).
The regulator 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 end of the electric fuel
pump.Refer to Fuel Pump - Description and
Operation for more information.
If fuel pressure at the pressure regulator exceeds
approximately 60 psi, an internal diaphragm opens
and excess fuel pressure is routed back into the tank
through the bottom of pressure regulator.
Both fuel filters (at bottom of fuel pump module
and within fuel pressure regulator) are designed for
extended service. They do not require normal sched-
uled maintenance. Filters should only be replaced if
a diagnostic procedure indicates to do so.
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 is supplied to the resistor track on the fuel
gauge sending unit. This is fed directly from the
Powertrain Control Module (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 models).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.
Fig. 2 SIDE VIEW - FILTER/REGULATOR
1 - INTERNAL FUEL FILTER
2 - FUEL FLOW TO FUEL INJECTORS
3 - FUEL FILTER/FUEL PRESSURE REGULATOR
4 - EXCESS FUEL BACK TO TANK
5 - FUEL INLET
6 - RUBBER GROMMET
7 - TOP OF PUMP MODULE
14 - 6 FUEL DELIVERY - GASDR
FUEL FILTER/PRESSURE REGULATOR (Continued)

stream. The spraying action atomizes the fuel, add-
ing it to the air entering the combustion chamber.
The nozzle (outlet) ends of the injectors are posi-
tioned into openings in the intake manifold just
above the intake valve ports of the cylinder head.
The engine wiring harness connector for each fuel
injector is equipped with an attached numerical tag
(INJ 1, INJ 2 etc.). This is used to identify each fuel
injector.
The injectors are energized individually in a
sequential order by the Powertrain Control Module
(PCM). The PCM will adjust injector pulse width by
switching the ground path to each individual injector
on and off. Injector pulse width is the period of time
that the injector is energized. The PCM will adjust
injector pulse width based on various inputs it
receives.
Battery voltage is supplied to the injectors through
the ASD relay.
The PCM determines injector pulse width based on
various inputs.
OPERATION - PCM OUTPUT
The nozzle ends of the injectors are positioned into
openings in the intake manifold just above the intake
valve ports of the cylinder head. The engine wiring
harness connector for each fuel injector is equipped
with an attached numerical tag (INJ 1, INJ 2 etc.).
This is used to identify each fuel injector with its
respective cylinder number.
The injectors are energized individually in a
sequential order by the Powertrain Control Module
(PCM). The PCM will adjust injector pulse width by
switching the ground path to each individual injector
on and off. Injector pulse width is the period of time
that the injector is energized. The PCM will adjust
injector pulse width based on various inputs it
receives.
Battery voltage (12 volts +) is supplied to the injec-
tors through the ASD relay. The ASD relay will shut-
down the 12 volt power source to the fuel injectors if
the PCM senses the ignition is on, but the engine is
not running. This occurs after the engine has not
been running for approximately 1.8 seconds.
The PCM determines injector on-time (pulse width)
based on various inputs.
REMOVAL
(1) Remove fuel rail. Refer to Fuel Injector Rail
Removal.
(2) Disconnect clip(s) that retain fuel injector(s) to
fuel rail (Fig. 12).
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 turned
ON, 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.
Fig. 12 INJECTOR RETAINING CLIP
1 - PLIERS
2 - INJECTOR CLIP
3 - FUEL INJECTOR - TYPICAL
4 - FUEL RAIL - TYPICAL
DRFUEL INJECTION - GAS 14 - 27
FUEL INJECTOR (Continued)

(3) Position sensor into intake manifold and rotate
clockwise until past release tab.
(4) Install electrical connector.
5.7L V-8
The intake manifold air temperature (IAT) sensor
is installed into the front of the intake manifold air
box plenum (Fig. 19).
(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.
MAP SENSOR
DESCRIPTION
3.7L V-6
The Manifold Absolute Pressure (MAP) sensor is
mounted into the front of the intake manifold with 2
screws.
4.7L V-8
The Manifold Absolute Pressure (MAP) sensor is
mounted into the front of the intake manifold with 2
screws.
5.7L V-8
The Manifold Absolute Pressure (MAP) sensor is
mounted to the front of the intake manifold air ple-
num box.
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
Fig. 20 5.7L IAT SENSOR R/I
1 - FRONT OF INTAKE MANIFOLD PLENUM
2 - IAT SENSOR
3 - RELEASE TAB
14 - 32 FUEL INJECTION - GASDR
INTAKE AIR TEMPERATURE SENSOR (Continued)