How to test O2 sensors?

Hey I am gonna be swapping in a different mid-pipe in a couple weeks. I want to test the O2 sensors and replace them while the exhaust is off, if necessary. How should I test them to see if they need replaced? Can I use a multi-meter or do I need to use a scan tool while they are still installed?

HISSIN50 said:

Using a scope/scan tool, etc is best, but you can get a crude idea from watching the switching with a meter.

As they age, they switch less quickly and with less amplitude.

I think you might kinda have to go with your gut on this one.

Good luck.

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I might just pick up a pair of new ones. I am pretty sure they are original (and the car has 114K on it). The reason I ask, is I got an Autometer A/F gauge about a month ago, just for kicks (I know they really dont show much unless you go to a wideband commander or similar setup). When it was all installed, I noticed the sweep was VERY slow and would hesitate sometimes at either end of the readout. So I re-checked all the connections, and everything was fine. I switched the source for the signal to the other O2 sensor, and the same result. This sort of made me think my O2's may be bad. Are there any noticeable symptoms of bad O2's?