The O2 sensor generates voltage in the range of about 0 to 1 volts. Higher voltages (greater than 0.5 volts) means there little or no O2 in the exhaust and indicates a rich mixture. Lower voltages (less than 0.5 volts) means there is a lot of O2 in the exhaust and indicates a lean mixture.
Check the number of "O2 cross counts" with a scan tool. This is the number of times the O2 sensor voltage crosses 450 mV in a sample period (which I believe is 10 seconds). The higher this number is the better. I think a good minimum is 10 but hopefully you'll see values above 20.
Although they don't last forever, O2 sensors are frequently replaced when still good. But if yours has white deposits on it, it's probably contaminated.
If you remove your O2 sensor and decide to reinstall it, make sure to use some of the special anti-seize (which is made out of tiny glass beads). New sensors come with it pre-applied. (But if you install and remove a new sensor, you need to apply more anti-seize!) The stuff I use is AC/Delco High Temp Anti-Seize Compound (part 5613695).
O2 sensors are another part your local
AC/Delco distributor has cheaper
than the dealer.
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