You can test the o2 with a voltmeter, I will tell you how.

Your o2 sensor reads 0-1 volt. It creates its own voltage. On a 4-wire o2 sensor, the o2 sensor wire that goes to the ECU (pin C18) is the WHITE wire. Take a voltmeter, or a multimeter set on DC 20 (Direct current, lowest voltage setting), and jab the red probe through the insulation on the white wire, touch the black probe to the (-) terminal on your battery. Watch the needle on the voltmeter. If it cycles up and down from 0-1 volt while your car is idling, it works.

The other alternative is to buy an Autometer Air/fuel gauge. It works off of the voltage from the o2 sensor wire. For installation, you need power, ground, and the last wire splices to pin C18 at your ECU. Really simple install, and the gauge is less than $60 if you shop around. There are cheaper ones out there, too, but the Autometer works really well, and will not only tell you your o2 sensor is working, but how rich or lean your car is running. A great tool for people with fuel economy issues, or for boost junkies.

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