Thanks, I did actually attempt to do a web search as suggested but I am afraid that Google seems to have gone badly downhill over the last 12 months or so. (All I seemed to be able to find was page after page of "Buy Avensis Lambda sensors at shopzilla.com" type nonsense.

We have decided to call it a day on the car on the grounds that I cannot be "Certain" that an expensive toyota cat will fix it. It is a shame though because it is otherwise a sound car!

It would be nice to be able to find out a more detailed explanation as to how this system actually works though if anybody does have some working links.

Paul