The CEL went on 5 miles after I left the service, not sure if they did something wrong or did this happen just by accident. They of course need to study it, but this is a bit more complex as the local dealer is not so skilled and next one is a bit far. Need to help them.

Went already and checked the how the catalycs are working and seems to be ok according to other place.

So it must be sensor problem like so many times with these CEL lights...just finally did got over the cooling system temperature sensor problem that was there too long (the first new sensor was invalid I guess).

Does anyone know where the sensor that these codes P0431, P1459 refer to are located? It's A6 2.7T 2001.
Could it be something else, like some air leak or some pipe broke/not in good shape...
and it sometimes does not run very well the first minute when it's cold. Sometimes it is just ok.