Ok so I'm a geek. I was actually reading the service manual just for the heck of it. I heard someone awhile ago claim that the rear O2 sensors would fine tune the fuel trim. I find this hard to beleive since I know that is what the front O2 sensors are for and after the cat there shouldn't be any gas. I didn't find anything about the rear O2 sensors controlling fuel trim but I did find this.

To monitor the system, the number of lean-to-rich
switches of upstream and downstream O2S’s is
counted. The ratio of downstream switches to
upstream switches is used to determine whether the
catalyst is operating properly. An effective catalyst
will have fewer downstream switches than it has
upstream switches i.e., a ratio closer to zero. For a
totally ineffective catalyst, this ratio will be one-toone,
indicating that no oxidation occurs in the device.


This makes sense. On my truck the rear O2 sensors just hang there. They were the universals that I used up front until I bought the ones that are non-universal. So these sensors are brand new and read a constant voltage of .2. This whole time I've been wondering why there isn't a code being set. Apperently because the rear isn't oscillaring it thinks that everything is good even though the sensor is reporting high oxygen. I'm guessing that if anyone has ever had a code set with the O2 sensors hanging out they were old sensors and were probably oscilating because they couldn't sense oxygen corectly.