Prizm L4-108 1.8L DOHC VIN 8 MFI (1998)
Oxygen Sensor: Description and Operation
Heated Oxygen Sensor 2 (HO2S 2)
Heated Oxygen Sensor 1 (HO2S 1)
Heated Oxygen Sensor 2 (HO2S 2)
The post catalyst (1) heated oxygen sensor 2 (HO2S 2) is located in the exhaust pipe after the catalytic converter. The powertrain control module (PCM)
uses the HO2S 2 in order to monitor the oxygen storage capability of the catalytic converter.
Operation
A three-way catalytic converter (TWC) is used in order to control the emissions of hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen
(NOx). The catalyst within the converter promotes a chemical reaction which oxidizes the HO and CO present in the exhaust gas. The catalyst converts
the HO and CO into harmless water vapor and carbon dioxide. The catalyst also reduces NOx by converting the NOx to nitrogen. The HO2S 2 reacts to
the oxygen content in the exhaust stream after it passes through the catalytic converter. The voltage signal created by the HO2S 2 sensor ranges from
approximately 0.1 volt (high oxygen - lean mixture) to 0.9 volt (low oxygen - rich mixture). The oxygen sensor heater is required for the catalyst monitor
HO2S 2 in order to become active and begin accurate catalyst monitoring. An HO2S 2 signal that appears lazy or inactive is normal. The PCM compares
readings from both the HO2S 1 and the HO2S 2 in order to determine the efficiency of the catalyst in the TWO converter.
In order for the HO2S 2 to function properly, the sensor must have a supply of clean reference air. Clean reference air is obtained through the oxygen
sensor pigtail wiring. Any attempt to repair the wires, the connectors, or the terminals of the HO2S 2 pigtail wiring could result in the obstruction of the
reference air. Replace the oxygen sensor if the pigtail wiring, the connector or the terminals are damaged. The oxygen sensor heater greatly decreases the
amount of time required for the HO2S 1 to become active and begin the closed loop fuel control.
The catalyst monitor heated oxygen sensor 2 (HO2S 2) is diagnosed for the following functions:
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A signal fixed low during steady state conditions or power enrichment (hard acceleration when a rich mixture should be indicated).
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A signal fixed high during steady state conditions or decel fuel mode (deceleration when a lean mixture should be indicated).
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The heater performance
