Info on O2 sensors from wikipedia.....Also how stuff works:
If you read through this little bit you will see that the O2 measures, well exactly what it says O2, then compares it with O2 going into the engine.
Temp "of the sensor" has little to do with it except to make sure its at it's operating temp so the readings are accurate.
Automotive applications
Automotive oxygen sensors, colloquially known as an O2 sensors or lambda sensors make modern electronic fuel injection and emission control possible. They determine if the air/fuel ratio exiting a gas-combustion engine is rich(unburnt fuel vapor) or lean(excess oxygen). Closed loop feedback controlled fuel injection means that the fuel injector output is varied according to real-time sensor data rather than operating with a predetermined fuel map (open loop). In addition to improving overall engine operation, they reduce the amounts of both unburnt fuel and oxides of nitrogen from entering the atmosphere. Unburnt fuel is pollution in the form of air born hydrocarbons, while oxides of nitrogen(NOX gases) are a result of excess air in the fuel mixture resulting in smog and acid rain producing compounds.
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.
Tampering with or modifying the signal that the oxygen sensor sends to the engine computer can be detrimental. 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 be a slight increase in power, again at the risk of overheating and igniting the catalytic converter, while decreasing fuel economy and increasing hydrocarbon emissions.
When an internal combustion engine is under high load (such as when using wide-open throttle) the oxygen sensor no longer operates (it works, but the signal isn't used to make adjustments in relation to fuel trim/control), and the engine automatically enriches the mixture to protect the engine. Any changes in the sensor output will be ignored in this state, while changes from the air flow meter can lower engine performance due to the mixture being too rich or too lean, and increase the risk of engine damage due to detonation if the mixture is too lean.
[edit] Function of a lambda probe
Lambda probes are used to reduce vehicle emissions, by ensuring that engines burn their fuel efficiently and cleanly. Robert Bosch GmbH introduced the first automotive lambda probe in 1976, and it was first used by Volvo and Saab in that year. The sensors were introduced in the US from about 1980, and were required on all models of cars in many countries in Europe in 1993.
By measuring the proportion of oxygen in the remaining exhaust gas, and by knowing the volume and temperature of the air entering the cylinders amongst other things, an ECU can use look-up tables to determine the amount of fuel required to burn at the stoichiometric ratio (14.7:1 air:fuel by mass for gasoline) to ensure complete combustion.
[edit] The probe
The sensor element is a ceramic cylinder plated inside and out with porous platinum electrodes; the whole assembly is protected by a metal gauze. It operates by measuring the difference in oxygen between the exhaust gas and the external air, and generates a voltage or changes its resistance depending on the difference between the two. The sensors only work effectively when heated to approximately 300°C, so most newer lambda probes have heating elements encased in the ceramic to bring the ceramic tip up to temperature quickly when the exhaust is cold. The probe typically has four wires attached to it: two for the lambda output, and two for the heater power, although some automakers use a common ground for the sensor element and heaters, resulting in three wires. Earlier non-electrically-heater sensors had one or two wires.
The whole article is here:
Oxygen sensor - Wikipedia, the free encyclopedia
