Volvo Repair: obd codes, vacuum line, p0442

Question
I recently bought a machine to analyze my car's computer and the check engine light that has been lit up for quite some time now.  I got the codes of po411, p0442, and po172.  I can read what the descriptions of the codes are but could you explain them in terms I could understand as someone who is a far cry from an expert?  Additionally, I went to get some works done a little while ago and the mechanic was pushing for me to get a new exhast system because of these codes...is that appropriate?  I took it as he was attempting to hose a college female and chose not to get the work done.  How serious are these codes, and are they all connected as the mechanic made them seem.


THanks

Answer
these codes do not really mean anything to me .when we use a volvo scan tool it gives different codes with more information.these are generic codes.I would have to find something at work to cross reference them.you also did not mention a year and model for the car.I do know the 172 codes is a fuel trim code which could be many things from a serious problem or just a bad vacuum line.I will need to try to check these codes at work or send me a description of them if possibl and maybe I will be able to offer some insite as to possible problems.