Chrysler 1997 Stratus Convertible RHD Service Manual page 885

JX
DESCRIPTION AND OPERATION (Continued)
ENGINE COOLANT TEMPER- ATURE SENDING UNIT
COOLANT
FILLER CAP
Fig. 6 Crankshaft Position Sensor—2.5L Engine
As coolant temperature varies, the coolant temper-
ature sensor resistance changes resulting in a differ-
ent current draw from the PCM.
When the engine is cold, the PCM will provide
slightly richer air- fuel mixtures and higher idle
speeds until normal operating temperatures are
reached.
The coolant sensor threads into the front of the cyl-
inder head 2.4L (Fig. 7); next to the coolant fill neck
2.5L (Fig. 8). New sensors have sealant applied to
the threads.
Fig. 7 Engine Coolant Temperature Sensor—2.4L
FUEL LEVEL SENSOR—PCM INPUT
The fuel level sensor (fuel gauge sending unit)
sends a variable voltage to the PCM to indicate fuel
level. The purpose of this feature is to prevent a false
setting of misfire and fuel system monitor trouble
codes if the fuel level is less than approximately 15
percent of its rated capacity.
Fig. 8 Engine Coolant Temperature Sensor—2.5L
HEATED OXYGEN SENSORS—PCM INPUT
As vehicles accumulate mileage, the catalytic con-
vertor deteriorates. The deterioration results in a
less efficient catalyst. To monitor catalytic convertor
deterioration, the fuel injection system uses two
heated oxygen sensors. One sensor upstream of the
catalytic convertor, one downstream of the convertor.
The PCM compares the reading from the sensors to
calculate the catalytic convertor oxygen storage
capacity and converter efficiency. Also, the PCM uses
the upstream heated oxygen sensor input when
adjusting injector pulse width.
When the catalytic converter efficiency drops below
emission standards, the PCM stores a diagnostic
trouble code and illuminates the malfunction indica-
tor lamp (MIL).
The automatic shutdown relay supplies battery
voltage to both the upstream and downstream heated
oxygen sensors. The oxygen sensors are equipped
with a heating element. The heating elements reduce
the time required for the sensors to reach operating
temperature.
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.
FUEL SYSTEM 14 - 31