What is the role of an oxygen sensor in measuring exhaust gas?

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The oxygen sensor plays a vital role in measuring the remaining oxygen in the exhaust gas after combustion and subsequently generates a voltage output of between 0.1 volt (indicating high oxygen, lean mixture) and 0.9 volts (indicating low oxygen, rich mixture). In early models (1988-1995), a single wire oxygen sensor is positioned in the exhaust pipe just after the exhaust manifold. In later models (1996-2000), there are four oxygens sensors with two of them being pre-converter oxygen sensors located before the catalytic converter. To regulate fuel injector pulse width, the PCM continuously monitors voltage from the pre-converter oxygen sensor in order to keep an air/fuel ratio of 14.7:1 which optimizes emission and performance of an engine. The post converter oxygen sensor however does not influence air/fuel ratio control but rather, it is used to monitor catalytic converter efficiency as evidenced by slower fluctuating voltage signals indicating low levels of oxygen after catalysts. Below this, during warm-up, there is no use for the sensor's feedback as ECM/PCM operates in open-loop mode. Oxygen sensors require heating elements to achieve operating temperature quickly. Proper sensor operation depends on electrical connections, adequate air supply, proper temperature and unleaded fuel usage. Oxygen sensors issues can be detected by ECM/PCM by setting diagnostic trouble codes known as DTCs relating to its malfunctioning or failure which can be determined by observing its response to input signal changes etc . When disconnecting it for testing purposes, extreme care should be taken to avoid damaging it and also provide jumper wires/backprobing under which case should not produce diagnostic trouble codes that are normally expected if one wants to do testing without risking any damage on car´s electric system although a diagnostic trouble code will still be triggered . With key on, voltmeter tests should indicate about 400-450 millivolts and for a warmed up engine, they should show voltage ranging from 100-900 millivolts for pre-converter sensors while post-converter sensors should show voltage within this range with no switching taking place. With the ignition on, in late models' oxygen sensor heater circuits it should be around 12 volts and heater resistance should be between 3.0 and 14.0 ohms. When replacing an oxygen sensor it must be done so that we do not damage pigtail and electrical connector, keep contaminants off of the sensor, avoid using cleaning solvents, and handle the sensor gently. Starting the engine briefly before replacement can ease removal. For secure removal of a post converter sensor, make sure that the vehicle is securely raised, disconnect the electrical connector if you are not quite sure how to use it yet, unscrew the sensor by employing your favorite tool for that purpose, apply anti-seize compound to its threads and then firmly fix it while reattaching its electrical connector after lowering down your vehicle.

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