they have to have ambient air on the back side of the element so that the oxygen gradient can be measured relative to "normal" While it may be unlikely that poisening will occure from this, it's not impossible.

Matt

 

If the sensing tip located inside the exhaust stream is subjected to anti freeze the sensor will be destroyed; a number of manufacturers recommend not using certain types of silicone based gasket sealants on the intake manifold or components that could otherwise facilitate a path to the o2 sensing tip.

If the cylinder head gasket is compromised A/F could find it's way into the combustion chamber, then its a short trip to the o2, my understanding is that the sensor is poisoned within minutes of this type of breach!

 

Ive noticed my coolant level is low lately, but I have not had any leaks since fixing my power steering leak. I also have an open circuit in my o2, and I am at 71k. I doubt it is related, as Silenpro has obnoxiously stated, but it is funny our cars have that commonground.