Dodge Durango (DN). Manual - part 16

ENGINE COOLANT TEMPERATURE SENSOR—
PCM INPUT

DESCRIPTION

The Engine Coolant Temperature (ECT) sensor is

used to sense engine coolant temperature. The sensor
protrudes into an engine water jacket.

The ECT sensor is a two-wire Negative Thermal

Coefficient (NTC) sensor. Meaning, as engine coolant
temperature increases, resistance (voltage) in the
sensor decreases. As temperature decreases, resis-
tance (voltage) in the sensor increases.

OPERATION

At key-on, the Powertrain Control Module (PCM)

sends out a regulated 5 volt signal to the ECT sensor.
The PCM then monitors the signal as it passes
through the ECT sensor to the sensor ground (sensor
return).

When the engine is cold, the PCM will operate in

Open Loop cycle. It will demand slightly richer air-
fuel mixtures and higher idle speeds. This is done
until normal operating temperatures are reached.

The PCM uses inputs from the ECT sensor for the

following calculations:

• for engine coolant temperature gauge operation

through CCD or PCI (J1850) communications

• Injector pulse-width

• Spark-advance curves

• ASD relay shut-down times

• Idle Air Control (IAC) motor key-on steps

• Pulse-width prime-shot during cranking

• O2 sensor closed loop times

• Purge solenoid on/off times

• EGR solenoid on/off times (if equipped)

• Leak Detection Pump operation (if equipped)

• Radiator fan relay on/off times (if equipped)

• Target idle speed

FIVE VOLT SENSOR SUPPLIES—PRIMARY
AND SECONDARY

DESCRIPTION

Two different Powertrain Control Module (PCM)

five volt supply circuits are used; primary and sec-
ondary.

OPERATION

These 2 circuits will:
• supply the required 5 volt power source to the

Crankshaft Position (CKP) sensor.

• supply the required 5 volt power source to the

Camshaft Position (CMP) sensor.

• supply a reference voltage for the Manifold Abso-

lute Pressure (MAP) sensor.

• supply a reference voltage for the Throttle Posi-

tion Sensor (TPS) sensor.

• supply the required 5 volt power source to the

oil pressure sensor.

• supply the required 5 volt power source for the

Vehicle Speed Sensor (VSS) (if equipped).

• supply the 5 volt power source to the transmis-

sion pressure sensor (if equipped with an RE auto-
matic transmission).

FUEL LEVEL SENSOR—PCM INPUT

DESCRIPTION

The fuel level sensor (fuel gauge sending unit) is

located on the fuel pump module.

OPERATION

Refer to Fuel Gauge Sending Unit in the Fuel

Delivery section for information.

IGNITION CIRCUIT SENSE—PCM INPUT

DESCRIPTION

This circuit ties the ignition switch to the Power-

train Control Module (PCM).

OPERATION

The ignition circuit sense input tells the PCM the

ignition switch has energized the ignition circuit.

Battery voltage is supplied to the PCM through the

ignition switch when the ignition is in the RUN or
START position. This is referred to as the “ignition
sense” circuit and is used to “wake up” the PCM.
Voltage on the ignition input can be as low as 6 volts
and the PCM will still function. Voltage is supplied to
this circuit to power the PCM’s 5 volt primary and 5
volt secondary circuits. This allows the PCM to per-
form fuel, ignition and emissions control functions.

INTAKE MANIFOLD AIR TEMPERATURE
SENSOR—PCM INPUT

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

14 - 32

FUEL SYSTEM

DESCRIPTION AND OPERATION (Continued)

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:
• Injector pulse-width

• Adjustment of spark timing (to help prevent

spark knock with high intake manifold air-charge
temperatures)

The resistance values of the IAT sensor is the same

as for the Engine Coolant Temperature (ECT) sensor.

MANIFOLD ABSOLUTE PRESSURE (MAP)
SENSOR—PCM INPUT

DESCRIPTION

The Manifold Absolute Pressure (MAP) sensor is

attached to the side of the engine throttle body with
2 screws. The sensor is connected to the throttle body
with a rubber L-shaped fitting.

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:

• Manifold pressure

• Barometric pressure

• Engine load

• Injector pulse-width

• Spark-advance programs

• Shift-point strategies (certain automatic trans-

missions only)

• Idle speed

• Decel 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.
The range of voltage output from the sensor is usu-
ally between 4.6 volts at sea level to as low as 0.3
volts at 26 in. of Hg. Barometric pressure is the pres-
sure exerted by the atmosphere upon an object. At
sea level on a standard day, no storm, barometric
pressure is approximately 29.92 in Hg. For every 100
feet of altitude, barometric pressure drops.10 in. Hg.
If a storm goes through it can change barometric
pressure from what should be present for that alti-
tude. You should know what the average pressure
and corresponding barometric pressure is for your
area.

FUEL SYSTEM

14 - 33

DESCRIPTION AND OPERATION (Continued)

OIL PRESSURE SENSOR—PCM INPUT

DESCRIPTION

The 2–wire, electrical/mechanical engine oil pres-

sure sensor (sending unit) is located in an engine oil
pressure gallery.

OPERATION

The oil pressure sensor uses two circuits. They are:
• A signal to the PCM relating to engine oil pres-

sure

• A 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.

OXYGEN SENSOR (O2S)—PCM INPUT

DESCRIPTION

The Oxygen Sensors (O2S) are attached to, and

protrude into the vehicle exhaust system. Depending
on the emission package, the vehicle may use a total
of either 2 or 4 sensors.

Non-California Engines: On certain non-Califor-

nia (Federal) emissions packages, 2 sensors are used:
upstream (referred to as 1/1) and downstream
(referred to as 1/2). With this emission package, the
upstream sensor (1/1) is located just before the main
catalytic convertor. The downstream sensor (1/2) is
located just after the main catalytic convertor.

California Engines: On certain California emis-

sions packages, 4 sensors are used: 2 upstream
(referred to as 1/1 and 2/1) and 2 downstream
(referred to as 1/2 and 2/2). With this emission pack-
age, the right upstream sensor (2/1) is located in the
right exhaust downpipe just before the mini-catalytic
convertor. The left upstream sensor (1/1) is located in
the left exhaust downpipe just before the mini-cata-
lytic convertor. The right downstream sensor (2/2) is
located in the right exhaust downpipe just after the
mini-catalytic convertor, and before the main cata-
lytic convertor. The left downstream sensor (1/2) is
located in the left exhaust downpipe just after the
mini-catalytic convertor, and before the main cata-
lytic convertor.

OPERATION

An O2 sensor is a galvanic battery that provides

the PCM with a voltage signal (0-1 volt) inversely
proportional to the amount of oxygen in the exhaust.
In other words, if the oxygen content is low, the volt-

age output is high; if the oxygen content is high the
output voltage is low. The PCM uses this information
to

adjust

injector

pulse-width

achieve

the

14.7–to–1 air/fuel ratio necessary for proper engine
operation and to control emissions.

The O2 sensor must have a source of oxygen from

outside of the exhaust stream for comparison. Cur-
rent O2 sensors receive their fresh oxygen (outside
air) supply through the wire harness. This is why it
is important to never solder an O2 sensor connector,
or pack the connector with grease.

Four wires (circuits) are used on each O2 sensor: a

12–volt feed circuit for the sensor heating element; a
ground circuit for the heater element; a low-noise
sensor return circuit to the PCM, and an input cir-
cuit from the sensor back to the PCM to detect sen-
sor operation.

Oxygen

Sensor

Heaters/Heater

Relays:

Depending on the emissions package, the heating ele-
ments within the sensors will be supplied voltage
from either the ASD relay, or 2 separate oxygen sen-
sor relays. Refer to Wiring Diagrams to determine
which relays are used.

The O2 sensor uses a Positive Thermal Co-efficient

(PTC) heater element. As temperature increases,
resistance

increases.

ambient

temperatures

around 70°F, the resistance of the heating element is
approximately 4.5 ohms on 5.2 and 5.9L engines, and
approximately 13.5 ohms on the 4.7L engine. As the
sensor’s temperature increases, resistance in the
heater element increases. This allows the heater to
maintain the optimum operating temperature of
approximately 930°-1100°F (500°-600° C). Although
the sensors operate the same, there are physical dif-
ferences, due to the environment that they operate
in, that keep them from being interchangeable.

Maintaining correct sensor temperature at all

times allows the system to enter into closed loop
operation sooner. Also, it allows the system to remain
in closed loop operation during periods of extended
idle.

In Closed Loop operation, the PCM monitors cer-

tain O2 sensor input(s) along with other inputs, and
adjusts the injector pulse width accordingly. During
Open Loop operation, the PCM ignores the O2 sensor
input. The PCM adjusts injector pulse width based
on preprogrammed (fixed) values and inputs from
other sensors.

Upstream

Sensor

(Certain

Non-California

Emissions): The upstream sensor (1/1) provides an
input voltage to the PCM. The input tells the PCM
the oxygen content of the exhaust gas. The PCM uses
this information to fine tune fuel delivery to main-
tain the correct oxygen content at the downstream
oxygen sensor. The PCM will change the air/fuel
ratio until the upstream sensor inputs a voltage that

14 - 34

FUEL SYSTEM

DESCRIPTION AND OPERATION (Continued)

the PCM has determined will make the downstream
sensor output (oxygen content) correct.

The upstream oxygen sensor also provides an input

to determine catalytic convertor efficiency.

Downstream Sensor (Certain Non-California

Emissions): The downstream oxygen sensor (1/2) is
also used to determine the correct air-fuel ratio. As
the oxygen content changes at the downstream sen-
sor, the PCM calculates how much air-fuel ratio
change is required. The PCM then looks at the
upstream oxygen sensor voltage and changes fuel
delivery until the upstream sensor voltage changes
enough to correct the downstream sensor voltage
(oxygen content).

The downstream oxygen sensor also provides an

input to determine catalytic convertor efficiency.

Upstream Sensors (Certain California Emis-

sions): Two upstream sensors are used (1/1 and 2/1).
The 1/1 sensor is the first sensor to receive exhaust
gases from the #1 cylinder. They provide an input
voltage to the PCM. The input tells the PCM the oxy-
gen content of the exhaust gas. The PCM uses this
information to fine tune fuel delivery to maintain the
correct oxygen content at the downstream oxygen
sensors. The PCM will change the air/fuel ratio until
the upstream sensors input a voltage that the PCM
has determined will make the downstream sensors
output (oxygen content) correct.

The upstream oxygen sensors also provide an input

to determine mini-catalyst efficiency. Main catalytic
convertor efficiency is not calculated with this pack-
age.

Downstream

Sensors

(Certain

California

Emissions): Two downstream sensors are used (1/2
and 2/2). The downstream sensors are used to deter-
mine the correct air-fuel ratio. As the oxygen content
changes at the downstream sensor, the PCM calcu-
lates how much air-fuel ratio change is required. The
PCM then looks at the upstream oxygen sensor volt-
age, and changes fuel delivery until the upstream
sensor voltage changes enough to correct the down-
stream sensor voltage (oxygen content).

The downstream oxygen sensors also provide an

input to determine mini-catalyst efficiency. Main cat-
alytic convertor efficiency is not calculated with this
package.

Engines equipped with either a downstream sen-

sor(s), or a post-catalytic sensor, will monitor cata-
lytic

convertor

efficiency.

efficiency

below

emission standards, the Malfunction Indicator Lamp
(MIL) will be illuminated and a Diagnostic Trouble
Code (DTC) will be set. Refer to Monitored Systems
in Emission Control Systems for additional informa-
tion.

POWER GROUNDS

OPERATION

The Powertrain Control Module (PCM) has 2 main

grounds. Both of these grounds are referred to as
power grounds. All of the high-current, noisy, electri-
cal devices are connected to these grounds as well as
all of the sensor returns. Sensor return is a low-
noise, low-current, dedicated ground.

The power ground is used to control ground cir-

cuits for the following PCM loads:

• Generator field winding

• Fuel injectors

• Ignition coil(s)

• Certain relays/solenoids

• Certain sensors

POWER STEERING PRESSURE SWITCH—PCM
INPUT

DESCRIPTION

A pressure sensing switch (Fig. 2) is included in

the power steering system (mounted on the high-
pressure line). This switch will be used only on vehi-
cles equipped with a 4.7L V–8 engine and power
steering.

Fig. 2 Power Steering Pump Pressure Switch—4.7L

V-8 Engine

1 – HYDRAULIC PUMP
2 – POWER STEERING PRESSURE SWITCH
3 – RACK AND PINION GEAR
4 – OIL COOLER

FUEL SYSTEM

14 - 35

DESCRIPTION AND OPERATION (Continued)

Content .. 14 15 16 17 ..