I've been watching my O2 sensor voltage recently with the AutoTap software and I've noticed strange trends. Here is what I've concluded:
Bank 1 Sensor 1: Constantly jumping between 75 mV and 845 mV
Bank 1 Sensor 2: Steady 750 mV with little change.
Bank 2 Sensor 1: Constantly jumping between 65 mV and 835 mV
Bank 2 Sensor 2: Same as B1S2, steady around 750 mV.
Does this seem normal? It doesn't sound right to me but I've never seen a check engine light.
Also, I just want to get my facts straight. Bank 1 is on the driver's side and Bank 2 is passenger side, correct? Sensor 1 is pre cat and Sensor 2 is post cat, correct?

 

That is what I see, don't pay attention to Sensor 2. Sensor 1 switches between rich to lean the entire time it is in closed loop. On an 04 your stock 02 switch points are 450mV. if you look at one of you sensors for example sensor 1 it has a high of 845 and a low of 75. So do the following math

Calculate entire range: 845-75= 770
Calculate half of the range: 7700/2 = 385
Add the starting point to half the range: 385+75 = 460

So your roughly at the switch point, you can adjust the switch point up and down to get a leaner or richer average mixture....... Make sense....

 

yup. Have a sensor 3?

 

OK, thanks BlackGMC! I thought the sensor reading would be more stable and not jump around from one extreme to the other. Sounds like everything is normal.

 

That's the way the narrowband O2's work....they are essentially like a switch that has two states...on or off. In this case, the switch can either be rich or lean. The PCM reads a lean condition and adds fuel until the O2 says rich. Then the PCM pulls fuel until the O2 says lean. Then the PCM adds fuel until it reads rich, and on and on.....that's why you see the O2 sensors doing that....it's the PCM cycling from rich to lean and back and forth over and over again....which keeps the actual AFR right around 14.7 where it needs to be.