Dodge ZB 2005 Service Manual page 811

14 - 38 FUEL INJECTION
O2 SENSOR (Continued)
UPSTREAM OXYGEN SENSOR
The input from the upstream heated oxygen sensor
tells the PCM the oxygen content of the exhaust gas.
Based on this input, the PCM fine tunes the air-fuel
ratio by adjusting injector pulse width.
The sensor input switches from 0 to 1 volt, depend-
ing upon the oxygen content of the exhaust gas in
the exhaust manifold. When a large amount of oxy-
gen is present (caused by a lean air-fuel mixture), the
sensor produces voltage as low as 0.1 volt. When
there is a lesser amount of oxygen present (rich air-
fuel mixture) the sensor produces a voltage as high
as 1.0 volt. By monitoring the oxygen content and
converting it to electrical voltage, the sensor acts as
a rich-lean switch.
The heating element in the sensor provides heat to
the sensor ceramic element. Heating the sensor
allows the system to enter into closed loop operation
sooner.
In Closed Loop, the PCM adjusts injector pulse
width based on the upstream heated oxygen sensor
input along with other inputs. In Open Loop, the
PCM adjusts injector pulse width based on prepro-
grammed (fixed) values and inputs from other sen-
sors.
DOWNSTREAM OXYGEN SENSOR
The downstream heated oxygen sensor input is
used to detect catalytic convertor deterioration. As
the convertor deteriorates, the input from the down-
stream sensor begins to match the upstream sensor
input except for a slight time delay. By comparing
the downstream heated oxygen sensor input to the
input from the upstream sensor, the PCM calculates
catalytic convertor efficiency. Also used to establish
the upstream O2 goal voltage (switching point).
REMOVAL
8.3L - UPSTREAM 1/1, 2/1
(1) Raise and support vehicle.
(2) Disconnect heated oxygen sensor electrical con-
nector (Fig. 17).
(3) Remove sensor using an oxygen sensor crow
foot wrench such as Snap-On tool YA8875 or equiva-
lent
8.3L - DOWNSTREAM 1/2, 2/2
(1) Raise and support vehicle.
(2) Disconnect heated oxygen sensor electrical con-
nector (Fig. 17).
(3) Remove sensor using an oxygen sensor crow
foot wrench such as Snap-On tool YA8875 or equiva-
lent
Fig. 17 2/1, 2/2, O2 SENSORS (Right Side)
1 - Upstream O2 Sensor
2 - Downstream O2 Sensor
INSTALLATION
8.3L - UPSTREAM 1/1, 2/1
(1) After removing the sensor, the exhaust mani-
fold threads must be cleaned with an 18 mm X 1.5 +
6E tap. If reusing the original sensor, coat the sensor
threads with an anti-seize compound such as Loctite
771- 64 or equivalent. New sensors have compound
on the threads and do not require an additional coat-
ing.
(2) Install sensor using an oxygen sensor crow foot
wrench such as Snap-On tool YA8875 or equivalent
(3) Tighten the sensor to 27 N·m (20 ft. lbs.)
torque.
(4) Plug sensor connector.
(5) Lower vehicle.
8.3L - DOWNSTREAM 1/2, 2/2
(1) After removing the sensor, the threads must be
cleaned with an 18 mm X 1.5 + 6E tap. If reusing the
original sensor, coat the sensor threads with an anti-
seize compound such as Loctite 771- 64 or equiva-
lent. New sensors have compound on the threads and
do not require an additional coating.
(2) Install sensor using an oxygen sensor crow foot
wrench such as Snap-On tool YA8875 or equivalent
(3) Tighten the sensor to 27 N·m (20 ft. lbs.)
torque.
(4) Plug sensor connector.
(5) Lower vehicle.
ZB