Hey guys/gals, I have a customers 2004 x type 2.5 with p0420, 0430, 0171 and 0174. I replaced the lower intake manifold gakets and got rid of 0171 and 0174. I replaced b2s2 and the front cat(radiator side) and got rid of p0430. obviously the only code left is 420. is it possible that both cats are bad? they were replaced 1 1/2 years ago. i know the front cat was bad because when i took it off and shook it, it sounded like marbles were inside. the readings on the bank one (firewall side) o2 sensors seem normal(b1s2 a little sluggish).... any thoughts?

 

If it's had unfixed lean (misfuel) codes long enough, then yes.