I've been looking through the Service Manual but can't work out for myself what the O2 sensors do.
Measure what? CO2, or Heat levels, and presumably feeback to the ECU to adjust Air Fuel Ratio?
Remember Martin that you have front and rear sensors which confuse a lot of peeps.
Alex, you ought to run a VQ35 masterclass for those of us who have a desire to learn all they can
but havn't historically had any mechanical experience.
As far as I was aware, I just have 2, as I have the stock cats - at the moment.
You will also have 2 front sensors in the exhaust manifolds mate.