It is possible to bench check an O2 sensor if you have a propane torch (no acetylene welding torches, they will destroy the sensor...)
Hold on a sec while I do a google search...
Here are some sites that detail the procedure:
http://www.shotimes.com/SHO3badO2sensor.html http://www.mr2.com/TEXT/O2_Sensor.html Note that on the 4-wire O2 sensors, the multimeter should be measuring the voltage from the black/grey wires.
The instructions say to hold the O2 sensor in a vise-grips and connect the ground from the multimeter to that.
I am not sure but I do not believe that 4-wire sensors are grounded that way because the 4th black wire is there to provide a more reliable ground than through the exhaust manifold, so hook the ground from the multimeter to the black wire.
Also check across the two white wires for resistance of a few ohms--this is the heating element connection, sometimes the element opens up and doesn't heat anymore. This will appear as infinite resistance and is sufficient cause for replacement.
Brian
