The foc-u font of all knowledge - misfuelling cockups....

[robby boy]

I would get the live data checked before replacing the cat, the diesel my have affected one of the oxygen sensors causing the code, is there any other codes? if you do a general check of that code it mentions the cat being clogged by oil, I dunno if the diesel would do the same, we had an old style corsa come in with the check engine light on, someone told us to remove the oxygen sensors an give them a good rub/clean on a wire brush then dip them in brake fluid, that did the trick (not that I'm saying that would work in this case). What type of car is it, try a quick google with the code and make / model.