I have a couple of used 4-wire O2 sensors here and I was wondering if there are any resistance test I can run on the sensor to check if it is still good?

 

I don't think you'll be able to get a reading from the O2 sensor signal wire. But you can get a resitance for the oxgen heater wires.. I think they're around 18 ohms.

Heater wires are the two common colors on each o2 sensor. Either 2 black or 2 white. The signal and signal ground are green/black or green/white.. once again differ in the years.. The signal could even be blue..but that may be Toyota.. can't remember

 

When the sensor is cold, the signal wire looks like an open circuit. It doesn't work until it gets hot.

Then put it in a car, warm it up, watch for the signal to swing quickly back & forth from 0.1 to 0.9 v.

 

i agree with jim usually you have to have a fluke or a really high quality meter to catch the switching becasue average switch time for a good O2 .05 seconds oscilloscopes work great but there expensive. yeah and an idea you smy want to try is recistance test a known good o2 versus the oens you are unsure of and use the good o2 for your benchmark

 

Throw the O2 in a bench vise and connect up the DMM to the white and green wires. Using a torch, heat the tip until you get a voltage then remove the flame and the reading should change. This won't tell you the speed at which the O2 can switch, but it does tell you it can generate the voltage.

You can also test the heater portion of it using the DMM: Just measure between the two black wires - 15-40 ohms is spec.