o2 sensor dose it sense air pressure

[Rodgebone]

oxygen sensors sample emission content only...they are designed and built with material and coatings that provide a chemical reaction which produce specific electrical outputs for the computer to sense to keep the air/fuel mixture as close to stoichiometric (14.7:1 air/fuel mix) as possible for the best fuel economy/power advantage/and acceptable emissions for the environment...they do NOT compare outside air content to emission content and are completely enclosed/sealed

[lawnman]

copied from wiki

An Oxygen Sensor is an electronic device developed by Volvo Car Corporation in the mid 1970s that measures the proportion of oxygen (O2) in the gas or liquid being analyzed. The sensing element is usually made with a zirconium ceramic bulb coated on both sides with a thin layer of platinum and comes in both heated and unheated forms. The most common application is to measure the performance of internal combustion engines in automobiles and other vehicles. Divers also use a similar device to measure the partial pressure of oxygen in their breathing gas.

Scientists use oxygen sensors to measure respiration or production of oxygen and use a different approach. Oxygen sensors are used in oxygen analyzers which find a lot of use in medical applications such as anesthesia monitors, respirators and oxygen concentrators.

There are many different ways of measuring oxygen and these include technologies such as zirconia, electrochemical (also known as Galvanic), infrared, ultrasonic and very recently laser. Each method has its own advantages and disadvantages.


[edit] Automotive applications
An automotive oxygen sensor, also known as an O2 sensor, lambda probe, lambda sensor, lambda sond or EGO (exhaust gas oxygen) sensor, is a small sensor inserted into the exhaust system of a petrol engine to measure the concentration of oxygen remaining in the exhaust gas to allow an electronic control unit (ECU) to control the efficiency of the combustion process in the engine. In most modern automobiles, these sensors are attached to the engine's exhaust manifold to determine whether the mixture of air and gasoline going into the engine is rich (too much fuel) or lean (too little fuel).

This information is sent to the engine management ECU computer, which adjusts the mixture to give the engine the best possible fuel economy and lowest possible exhaust emissions. Failure of these sensors, either through normal aging, the use of leaded fuels, or due to fuel contamination with eg. silicones or silicates, can lead to damage of an automobile's catalytic converter and expensive repairs.

A side-effect of oxygen sensors is that they can prevent fuel-saving technologies which create a lean fuel-air mixture from working. If the engine burns too lean due to any modifications, the sensor will detect the mixture as being too lean, and the engine computer will adjust the injector pulse duration, so that the air-fuel mixture continues to stay within the stoichiometric ratio of 14.7:1 on a typical vehicle. There are ways that the oxygen sensor can be overcome. Sometimes, a device can be inserted inline with the sensor, which tricks the engine computer into thinking the mixture is stoichiometric, when actually it is either rich, or lean, and therefore, this modification will not be automatically corrected by the oxygen sensor.

There are downsides of modifying the signal that the oxygen sensor sends to the engine computer. When the engine is under low-load conditions (such as when accelerating very gently, or maintaining a constant speed), the engine is operating under 'closed-loop mode'. This refers to a feedback loop between the fuel injectors, and the oxygen sensor, to maintain stoichiometric ratio. If modifications cause the mixture to run lean, there will be a slight increase in fuel economy, but with massive nitrogen oxide emissions, and the risk of damaging the engine due to detonation and excessively high exhaust gas temperatures. If modifications cause the mixture to run rich, then there will appear to be a slight increase in power, again at the risk of overheating and destroying the catalytic converter, and dramatically decreasing fuel economy while increasing emissions.

When an internal combustion engine is under high load (such as when using wide-open throttle) the oxygen sensor no longer operates, and the engine automatically enriches the mixture to both increase power and protect the engine. Any modifications to the oxygen sensor will be ignored in this state, while modifications to the air flow meter will give the risk of lower performance due to the mixture being too rich or too lean, and give the risk of damaging the engine due to detonation if the mixture is too lean.