O2 Sensors
 

I just received some used pipes & they still have the O2 sensors in them. Is there a way to test them to see if they still work?

You would have to install them, measure their ouput and compare to the readings of other O2 sensors. Not very scientific, but without a lab and a controlled environment it's a crapshoot.

O2 sensors are very reliable devices. However they're like the rest of us and get 'sluggish' with age. They also don't like to be handled roughly, so if the pipes have been subjected to a lot of banging around I'd give them a 50-50 chance.