I have just bought a second hand exhaust 'Y' pipe and cats for my 4.6 HSE, and in very good nick it is too, for =A350. It is the correct older type with just the two 12mm lambda sensors in front of the cats. However (there is always a 'however') the pipe has another single sensor under the left pipe AFTER the cat, but nothing on the right.
This additional sensor is still in place and has four wires but no plug. Any ideas what it is for as I was under the impression that later models and US market had TWO additional sensors after the cats.
AlunP