CEL CODES P0420, P0402

P0420 - catalyst system efficiency below threshold - bank 1
1) air leak in exhaust before rear H02s bank 1
2) af sensor error
3) fuel system fault
4) faulty cat
P0402 - system fault exhaust gas recirculation - too much flow on EGR
1) EGR valve stuck open
2) failed EGR pressure sensor, or valve or pressure sensor

thats whats i got this morning and was going to take a look at it this afternoon but i dont know where to start. any help would be appreciated...im pretty handy so i think i can get it fixed but just not sure where to begin....any one had these problems before?

 

may be 02 sensor. but its probably your cats. problem is if it is your cats you'll have to get factory ones, which are like a grand each