the check light came on on my mazda protege and when the mechanic checked it it was the nox sensor. the vehicle is working fine but the mechanic is telling me that i need to replace the nox sensor. my friend had a similar problem with his vehicle but his vehicle could not drive and hereplace the sensor now his vehicle is working perfect. the thing is that my vehicle is working perfect now. what is the purpose of the nox sensor and what relation does it have to the catalyst converter. can someone help me

 

Ur nox sensor allows a closed loop control to reduce emissions. some cars run when they aren't working, some don't.

In gasoline engines which operate on lean fuel mixtures, the lean combustion conditions produce nitrogen oxides, called NOx, in the exhaust gas stream, which must be removed because of their damaging effects on the environment. NOx accumulating catalytic converters in which an NOx accumulator in the catalytic converter stores the NOx during lean-mixture operation and releases it again during rich-mixture operation of the engine are preferably used to remove nitrogen oxides from lean exhaust gas. During this process, the NOx is reduced in the catalytic converter by the reducing constituents contained in the rich mixture exhaust gas

see: http://www.patentstorm.us/patents/64...scription.html

also..isn't the expression "REEK havoc"?

 

The Sensors are usually known as O2 or Lamda sensors. There are two. The one closest to the exhaust manifold is the active sensor; its output is fed to the ECU to modulate the air fuel mixture regime to achieve the 14.7:1 ratio for optimum combustion.
Next in line is the catalytic converter which extracts the residual hydrocarbon.
Following the cat. is the second sensor, whose job it is to measure residual combustibles and its output is an indication of how good a job the engine systems and cat. are doing. If the engine is off-tune, the cat. is no good OR IF YOU HAVE AN EXHAUST LEAK in the upstream side, this downstream sensor will respond accordingly. It is this sensor which makes the call on whether or not to turn on the CEL.
After a lot of use, the O2 sensors become insensitive and give rise to problems.
A useful trick is if you have to change only one sensor, always put the newest O2 sensor in the position closest to the manifold. That way you'll have the best sensor running the engine while the sloppy one will be the most tolerant of your emissions.