Stratus L4-2.4L VIN X (1998)
Oxygen Sensor: Description and Operation
Fig 11 Upstream Heated Oxygen Sensor
OPERATION
As vehicles accumulate mileage, the catalytic convertor 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 converter, one downstream
of the converter. 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
indicator 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, depending upon the oxygen content of the exhaust gas in the exhaust manifold. When a large amount of
oxygen 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. 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 preprogrammed (fixed values and inputs from other sensors.
The upstream oxygen sensor threads into the outlet flange of the exhaust manifold (Fig 11).
Fig 13 Downstream Heated Oxygen Sensor 1/2
