Neon L4-2.0L SOHC (1995)
Fig. 12 Upstream Heated Oxygen Sensor
HEATED OXYGEN SENSORS-PCM INPUT
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.
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One sensor upstream of the catalytic convertor
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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
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.
PURPOSE
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.
OPERATION
The sensor input switches from 0 to 1 volt, depending upon the oxygen content of the exhaust gas in the exhaust manifold.
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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.
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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.
Heating Element
The heating element in the sensor provides heat to the sensor ceramic element.
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Heating the sensor allows the system to enter into closed loop operation sooner.
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Also, it allows the system to remain in closed loop operation during periods of extended idle.
Closed Loop Operation
In Closed Loop, the PCM adjusts injector pulse width based on the upstream heated oxygen sensor input along with other inputs.
Open Loop Operation
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. 12).
CIRCUIT OPERATION:
The downstream oxygen sensor is a voltage generating device. The PCM receives exhaust gas information from this O2 sensor. The sensor detects
exhaust gas content by a galvanic reaction within the sensor that produces a voltage. After measuring the amount of oxygen in the exhaust gases,
the downstream oxygen sensor tells the PCM how well the catalytic converter is oxidizing HC and CO components and reducing NOx components
in the engine exhaust gas. This O2 sensor serves as an indicator of oxygen content. The heater element helps the O2 sensor quickly reach a normal
and steady operating temperature, which is required for proper emission control.
