I can not answer your vehicle specific questions but, I can tell you a little about pre-cat and post cat O2 sensors.
The pre-cat O2 feeds information ( oxygen content ) to the ECU, based on which the ECU feeds more or less fuel into the engine.
The post-cat O2 measures oxygen content again and feeds that information to the ECU as well.
The difference is the cross-counts ( rich/lean transitions) going to the ECU.
While the transitions are very rapid on the pre-cat O2, the post-cat transitions are much slower.
Makes sense, fuelmixture changes take effect instantly, converter changes take effect in a much more " lazy" manner.
Confused yet ?
