Car Oxygen Sensors

The amount of Oxygen leaving combustion chambers is one of key parameter to determine whether an engine operates at its optimum performance. There is a range of acceptable residual Oxygen portion within the exhaust gases for normal combustion process; too little or too much proportion beyond such range indicates either the engine is running too rich or lean of fuel to air mixture. A perfect air to fuel mixture must always follow Stoichiometric coefficient of 14.7.

In fact most AFR devices  actually measure exhaust gases either for the proportion of unburnt hydrocarbons to indicate rich mixtures combustion or the amount of residual oxygen in the case of lean mixture. Current standard practice is to measure how far from stoichiometric coefficient that mixture is; or known as Lambda (λ). Lambda of 1.0 indicates the air to fuel mixture is at stoichiometry, where as lean mixtures are greater than 1.0 and rich mixtures are less than 1.0,.

The Car Oxygen Sensor is mounted at exhaust manifold for non-turbo engine (schematic diagram). As the exhaust gas passes the sensor; any oxygen molecules will react with zirconium sensor to produce a small current. The presence of oxygen residual will trigger a signal to ECU for any proper air/fuel mixture requirements imprinted on its mapping database; the ECU or Engine Control Unit then compensate the fuel delivery to adjust. However under full throttle load such signal will be completely ignored and instead a rich mixture is induced to the combustion chambers in order to protect engine from knocking, similarly for cold start condition.

The exhaust manifold has a harsh condition for any sensor to age prematurely. Internal corrosion and old harness may hamper good grounding rendering error signal to be sent. Voltage loss due to wear and tear is the common source for such error as well, causing even a properly functioning sensor to not perform as it should do. A good voltage test on later model sensor will signal either lean or rich mixture as less than 0.352v or more than 0.547v, where as in between ECU considers engine to operate under normal air to fuel mixture.

There is a special care need to be followed for a proper Oxygen Sensor replacement procedure on any universal, OEM as well as aftermarket replacement. The choice of brand could be an overwhelming, but the easiest one would be to stick to your car manual guide. Regardless of the brand whether Denso, Delphi or Bosch Oxygen Sensorsyou would still need to go to your favorite car parts shop such as Autozone or the like for any technical consultation including the required Oxygen Sensors replacement tool.

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