[THEFERMANATOR]

Originally Posted by C YENSEN

my check engine light keeps coming on in my explorer...had the code read and it is a bad oxygen sensor. Will this affect my fuel mileage?

What year exploder? What engine? How many miles? Yes they can just fail, most times a cleaning does nothing for them long term. And remember that a code is just a diagnostic tool, not a definitive answer. Many other things can throw an O2 sensor code as well. If the O2 did in fact fail and go to an open circuit, then the PCM will not have any data to adjust the fuel mixture for changes and can seriously affect your milage. Like Franco said, it is basically a fine piece of wire that reacts to temperature and changes the voltage that it can conduct and relays the voltage change to the PCM to tell it what the fuel mixture is. Also most O2 sensors since the late 80's are now heated so they can give better readings at low engine output levels. If the heating element burns out this can also throw an O2 sensor code, but will not affect your cruising milage that much going down the road.

This is why most shops hate AUTOZONE who tells people they have an O2 code and say a new one will fix it. Something like a blown exhaust gasket, plugged cat converter, weak plygs, plugged fuel injectors, blown intake gaskets, or even a blown head gasket could show up as an O2 code. I even had one truck one time that had a bad coolant temp sensor and a stuck open thermostat pop an O2 sensor code, yet the O2 sensor was fine. The engine was running too cold and couldn't burn the fuel which in turn popped an O2 code.