Has any one had there nox sensor changed on the octivia mk3 diesel at all?

Mines gone back to the dealer for its 2nd!

Is it common for them to fail so often?

I think you have been super unlucky for two failing Lambada sensors but you are hopefully aware that there are a couple of Lambada sensors on the exhaust. Maybe you had two bad ones.....

 

Try not to do short journeys if possible. The Lambada sensors can get saturated with carbon and soot and fail if the combustion temperatures are not hot enough. 

Im lucky that i do about a 1000 miles a week and not doing a short  journeys