My sevice engine soon light came on the other day at 30k. i took it to autozone and the troubleshooting code P0420 came up. it says catalyst efficiency low bank 1. i figured that was goona b the problem cause i have stillen hfc's, but i put them in over 2 mnths ago and this just happened today. im wasent that worried untill i seen the probable causes. 1. engine misfire or running condition 2. large vacuum leak 3. engine oil leakage into exhaust, valve guide seals, piston rings. should i be concerned and get it checked? has this happened to n e one else? will the ses always stay on now?

 

Even though they are hi-flow cats they are still prone to throwing a P0420 or P0430 code. Try the non-foulers, they may work. Just clear the code and go on.