Fault Code P0174 anyone help?

[Condor]

I had forgotten that we had a generic fault code reader at home, so plugged it into the S8 this am to see if I could shed some light on the Engine Management Light suddenly coming on - it's given a Fault Code P0174 System too lean Bank 2, whatever that means - could one of the more knowledgeable members give me some info on this and if its serious / expensive / urgent or not?

After three weeks of no success trying to find a local Audi tech, when I realised we had the reader, I thought I'd check and see what it said........