I was told that since I didn't have a o2 sensor after my 2nd cat that I could remove the 2nd cat. My exhaust was in pretty bad shape so I had it replaced with a flowmaster 40 1 in 2 out and removed the 2nd cat. It has been like this for about a month no problems and no CEL. I was charging my a/c and spotted the white vacuum hose that seems to break on everyone. I fixed the hose and the next time I drove it the CEL came on. I pulled the codes and got a 634(mlps),311( thermactor air system inoperatable), 332 (egr insufficient flow). I replaced the mlps and that code is now gone. I was gonna start replacing the other parts but if the 2nd cat being gone is what is causing the problems then no since in replacing the sensors or other parts. Can anyone tell my if the 2nd cat being gone can cause these codes?