Nissan 226A0-AR210 Heated Oxygen Sensor

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The oxygen sensor in the exhaust system is responsible for controlling the air/fuel mixture in the engine. It generates voltage output varying between 0.1volt (indicating a lean mixture with high oxygen) and 0.9volts (indicating a rich mixture with low oxygen). The upstream oxygen sensor sends this feedback signal to the PCM which adjusts fuel injector pulse width and air/fuel ratio accordingly to keep a 14.7:1 air-to-fuel ratio that is considered ideal for emissions, fuel efficiency and performance of an engine. However, unlike its similar operation to the upstream sensor, the downstream one serves as a catalyst monitor rather than directly controling of air/fuel ratio. After this it keeps detecting lower levels of oxygen subsequent to a catalyst making more slowly oscillating voltage signals. Therefore through such signals, PCM can set Diagnostic Trouble Codes (DTCs) that help identify particular faults in any given oxygen sensors. When below its operating temperature of about 600°F (318°C), during warm up cycle of a sensor, the PCM operates in open-loop fuel control mode where it does not use feedback from the O2 sensor for air/fuel ratio adjustment relying on other sensors inputs and its program alone instead. Electric connections, appropriate operating temperatures, reaching proper operating temperature and using only lead-free fuels are some factors necessary for correctly performing O2 sensors' functions. However if a fault is detected by PCM , it changes back open loop fuel control since it will be forced to use DTCs indicating specific fault that may have been reached because of an open circuit or short circuit condition occurred on an oxygen sensor's side . While testing an O2 sensor, one should avoid damaging circuits by using digital voltmeter because this will prevent circuit damage as well as protect any attached electronic components like relays thereby avoiding starter failure since excessive current would damage them beyond repair. The white wire terminal at the oxygen sensor connector is backprobed and the positive lead of the voltmeter is connected to the probe while the negative lead is connected to a suitable engine ground. From this point, the engine is started and warmed up to normal operating temperature. The voltage of the oxygen sensor signal voltage is then checked. Upstream sensors should produce an actively switching voltage that ranges between 100 to 900 millivolts whereas downstream sensors should simply have any value between 100 to 900 millis and exhibit no active switching i.e. remaining mostly around 400 millivolts for long periods of time. Furthermore, it is important that battery supply and ground circuits through oxygen sensor heaters be checked by testing for approximately battery voltage at approximately with ignition switch ON and electrical connector unplugged as well as grounded leads using a voltmeter. A battery voltage supply from ignition switch can be measured by disconnecting electrical connector from an O2 sensor heater lead then grounding one meter lead and placing the other terminal on disconnected terminal whilst key in ON position (Zoebisch, n.d). Depending on model year, ohmmeter should be connected to two heater terminals of oxygen sensor side of connector which shows specific resistance values. Resistance can also be tested across both heater wires of the O2 sensor with an ohm meter (specific resistance values will depend on the model year) .In case it indicates open circuit or if there's more than three ohms resistance, then it implies that this device got out of order. If a scan tool reveals functional operation of an O2 sensor while there are still driveability problems or DTCs remains the same, then one needs to inspect all wiring harnesses visible between PCM and O2 sensors for opens or shorts before seeking assistance from dealer service department or qualified repair shop if they will find none. When replacing an oxygen sensor,it's better if you just turn on your car for a short period so as to help reduce the diameter of the exhaust pipe when cold. It is important to avoid damaging electrical connector and pigtail that are attached to the sensor, contamination and cleaning solvents, which should be done gently. Lastly , after installing the sensor ,it must be tightened securely and anti-seize compound applied to threads to facilitate removal in future.