Chrysler PT Cruiser Service & Repair Manual page 1338

14 - 42 FUEL INJECTION
O2 SENSOR (Continued)
The sensor input switches from 0 to 1 volt, depend-
ing upon the oxygen content of the exhaust gas in
the exhaust manifold (this is offset by 2.5 voltage on
NGC vehicles). When a large amount of oxygen is
present (caused by a lean air-fuel mixture), the sen-
sor produces voltage as low as 0.1 volt. When there is
a lesser amount of oxygen present (rich air-fuel mix-
ture) the sensor produces a voltage as high as 1.0
volt. By monitoring the oxygen content and convert-
ing 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. Also, it allows the system to remain in closed
loop operation during periods of extended idle.
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
REMOVAL - 1/1 UPSTREAM
(1) Remove the air cleaner lid and makeup air
hose.
(2) Remove the negative battery cable.
(3) Disconnect electrical connector from sensor.
(4) Remove sensor using an oxygen sensor special
tool C-4907 (Fig. 42).
REMOVAL - 1/2 DOWNSTREAM
The downstream heated oxygen sensor threads into
the exhaust pipe behind the catalytic convertor (Fig.
43).
(1) Remove the air cleaner lid and makeup air
hose.
(2) Remove the negative battery cable.
(3) Raise vehicle and support.
(4) Disconnect electrical connector from sensor.
(5) Disconnect sensor electrical harness from clips
along body.
Fig. 42 Oxygen Sensor 1/1 Upstream
1 - DOWN STREAM O2 SENSOR
2 - UP STREAM O2 SENSOR
Fig. 43 Oxygen Sensor 1/2 Downstream
1 - DOWN STREAM O2 SENSOR
2 - UP STREAM O2 SENSOR
(6) Remove sensor using an oxygen sensor crow
foot wrench such as Snap-On tool YA8875 or equiva-
lent (Fig. 44).
REMOVAL - 2.4L TURBO
(1) Disconnect the negative battery cable.
(2) Unlock and disconnect the electrical connector.
It is on the passenger side near the EVAP purge sole-
noid.
(3) Raise vehicle and support.
PT