p0420 code all stock 04 wrx minus a cbe
i just got my 2004 wrx about two weeks ago i installed a non name brand cat back exhuast drove roughly a tank of gas through it no problem noticed i was getting bad mpg so i cleaned my maf and reset the ecu. when i turned the car back on there was a cel. i again reset the ecu and no light came on i drove it for about a week. 300 miles or so then the cel came back on it was a p0420 i reset the ecu and its been off for about 50 miles or so. im new to subaru and the autozone people are no help, could this hurt my car and what could be setting it off. everything else is bone stock. ive researched all wrx forums but most everyone else with this code has a up pipe or aftermarket dp is it something simple or am i endangering my car by still driving it daily?!Cry!