I had thought that there are three sensors in the 2.7 but I can't find any, even on the parts diagrams. Where on earth is the oxygen sensor located?

I am installing the HHOPlus DC3000 hydrogen/Oxygen generation apparatus. I need to shade the lambda sensor. I have the shade device with the kit but I cannot make out which sensor it actually is. Once I have completed the modification (all the plumbing and electrics are installed, i went for the Pulse Width Modulator to control eneregy also if you are intersted). I just need to make some low level mods to the sensor arrangment and then I should be able to charge the system with electrolyte and see if the device yields the results.