E46 330Ci post-cat lambda sensor fault

[Chris71]

I thought I'd download the Carly diagnostics app and have a play. Sure enough, it picked up 21 fault codes first time round! They have all cleared and stayed clear, apart from the following:

00003D - Lambda probe heater after cat bank 2

There are no warning lights on the dash or anything like that and the original log didn't include any other engine-related codes. I've had a bit of a Google and it would appear the post-cat lambda sensors are only really there as a diagnostics function to flag up if the cat fails. Anyone know if that's true?

If so, presumably there's no great urgency to get it done? Anyone know how easy the post-cat sensors are as a DIY job and how you would work out which is 'bank 2'?