Neon L4-2.0L SOHC (1995)
Oxygen Sensor: Description and Operation
Oxygen Sensor Description
Downstream Oxygen Sensor
Fig. 13 Downstream 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 downstream heated oxygen sensor threads into the outlet pipe at the rear of the catalytic convertor (Fig. 13). The downstream heated oxygen
sensor input is used to detect catalytic convertor deterioration.
As the convertor deteriorates, the input from the downstream 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.
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.
Upstream Oxygen Sensor
