Sooty rear o2 sensors

[MDMetal]

Continuing my little saga of trying to tidy up faults.. My battery died about two weeks ago and the reset my cell so I figured after a year or so of ignoring to see what the current codes were... 

 

P0158 O2 Sensor Circuit High Voltage (Bank 2 Sensor 2)

 

P1166 - HO2S 2 bank 2 - minimum voltage

 

So its the same sensor. I lifted the car and removed both rear sensors they both look very sooty and very black. I'd seen a video where someone was saying you should be able to measure resistance across the two black wires, well I tried the black and the grey and the black vs everything else, infinite resistant is that a valid test? 

 

Given my issues with using lots of oil and looking at photos of oil contaminated sensors is it possible that my oil issues caused the sensors to fail and not the hfcs? If so sorting the oil issues and replacing the sensors is a sensible direction rather than just ignore the sensors? 

 

[andybp]

The 2 colours that are the same both black or both white usually should be the heater which is easy to check not sure what it should read though at a guess I'd say 3-5 ohms

[MDMetal]

Yah looks like that's what they're reading so the heater circuit is fine. I assume there's no way to test the rest of the sensor? So ruled out the heater circuit, either the sensor itself is broken or the oil is causing issues or the hfcs just really really don't like them

[MDMetal]

In case anyone ever stumbles over this. I replaced the rocker covers which had been leaking and causing lots of oil in the plenum and I've yet to have the 02 light come on so no doubt a ton of burnt oil was making it's way over to the sensor and causing issues. If you've an o2 sensor that constantly trips with HFC's then I'd recommend checking your Plenum to see if things are leaking