Power Grounds - Dodge 2000 DURANGO Service Manual

DN
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
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. If efficiency is 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.
(Certain California

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