Offroad-Express

Gidday,
In the process of ripping out the exhaust on my 94 Terrano and I found these. One of them has to be an o2 sensor?? (big one?) But what about the other one?? (small one?)
It is a vg30e motor and manual.
Cheers.
Josh.

small one is a cat "overheat" sensor.

The small one does nothing other than turn on the cat temp light on the dash .
The big one is for closed loop fuel trim at idle /cruise . Saves you gas