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Monkey_Man
Dodge Dakota
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9/18/2003
06:37:15
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 Subject: how does an O2 sensor work?
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Message:
Hello,
does anyone know how an O2 sensor works> I just changed mine abour 5,000 miles ago, everything is still running fine. I'm just racking my brain as to how it works.
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bskarger
Dodge Dakota
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9/18/2003
09:28:28
| RE: how does an O2 sensor work?
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Message:
Well, from what I understand...and I'm not an expert by any means...it measures the amount of oxygen in the exhaust, and converts that measurement into a voltage...higher voltage for a righer mixture, lower for a leaner mixture. The PCM looks at this voltage and adjusts the fuel/air mixture for optimum combustion. There is also a sensor after the catalytic converter which basically works in unison with the one in front of the cat...it checks to make sure the exhaust is cleaner than before it went into the cat.
...or something like that...
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Joe
Dodge Dakota
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9/18/2003
09:28:52
| RE: how does an O2 sensor work?
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It monitors the air temperature. Some trucks have one after the cat and some have several before and after the cat. The exhaust should be hotter after it goes through the cat, because the cat is a catalyst.
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Jon
Dodge Dakota
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9/18/2003
12:36:57
| RE: how does an O2 sensor work?
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Message:
It's true the exhaust is a couple hundred degrees hotter on the rear of the cat than on the front but the o2 doesn't measure temp. The o2 sensor has an atmospheric port that monitors the oxygen content of the air outside the exhaust, then it compares that air to the exhaust gas and creates voltage (like a battery) depending on the difference in oxygen between outside air and the oxygen in the exhaust gas. The o2 sensor reads .45 volts at stoichiometric, but the computer constantly switches the a/f ratio between rich and lean so you should see your front o2 sensor voltage vary between .35 and .85 volts about once per second. OBDII vehicles have an o2 sensor after the cat and it compares the voltage output of the rear sensor to the front sensor to see if the cat is working, the rear sensor voltage should vary up and down the slightest bit, if it starts to mimic the front sensor the computer will determine that the cat is dead or missing and give you a trouble code.
Also o2 sensors need to be at atleast 400 degrees farenheit to work so many of them have a 2 amp heater element to heat them up quickly.
Newer vehicles use a more accurate (and more expensive) air/fuel ration sensor instead of an o2, and those work completely different.
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