Code p0420 check engine light on. info says cat effic below threshold (bank 1). have been told that this is the cat next to motor. need to buy from dealer because it comes with manafold and cat. price could be $600.00 to $700.00 dollars to fix. this is big money for my budget. I had check engine light turned off but I know from past exp that it will come back on again soon.I have been told that this will decrease my gas milage by maybe 2 miles per gallon. and if not fixed could cause bigger problem down the road. p.s. this is in california. car passed smog check in between check engine light on and off period. thanks bob cali.