I have a V6 engine where one of the downstream O2 sensors reads .005v cold and KOEO. During sensor warm up it will be ~.005v higher than the other downstream sensor. After the engine is hot, and the engine is turned off, both sensors will read >0 (something like .007 to .003).

.005v is really low. Does it matter? Is it a sign that the sensor is going bad?

 

Both of my O2 sensors were reading .45V with KOEO (after sitting overnight). Is this typical of narrow-band O2 sensors?

After I started the engine, they seemed to behave normally.

 

Does this have anything to do with a Hummer? Since none have a V6 I think you are asking questions on the wrong forum site and we can't answer because we do not know what the vehicle is to determine if your voltage is in spec.

 

This is about my H3 I5.