B4 you flame me for asking a stupid question, I know what the O2 sensors measure, but how? Isn't it basically a resistor, calibrated to correllate specific levels of O2 in the exhaust to an ohm range? That's why o2 simms work, they "trick" the PCM by looping a specific millivolt range to the computer, which the PCM accepts, and thinks everything's hunky..right?