We keep getting the P0420 bank 1 and 2 codes on our 2001 QX4. I changed the 02 sensors and the codes still came back.

I was clearing the code every 2 weeks with our scanner and now if I clear it, it will reappear in less than 24 hours.

Our local shop says the catalytic converters need to be replaced.

So.. before I go ahead and order two new Cats, I wanted to get some opinions.

Also, I wanted to see where to buy a Stillen or other aftermarket exhaust system for the 3.5 liter QX4? Anyone sell high flow cats?

Thanks again for any help or suggestions. This is just our daily driver but some small mods would freshen it up a bit. So far all we have done is fog light bulbs, wheels, and intake. I do have a project car that I mod the heck out of and used to own a 1991 300ZX Twin Turbo and a 1996 Infiniti I30 in the past (among many other cars).



Take care,Elias

I don't know how a 2001 Infiniti could possible already have bad cats, but that is what P0420 means. Buying used cats is illegal, but I bought one from a junkyard for $75 once, I just had to be real discreet about it and prove that I wasn't a bust.

replacing your cats is a good idea but its just not so easy if you brought it for a cheaper price.When modifying your vehicle its not just from the transmission.Good tune up for your car is vital same as to dynomax exhaust.

We already did the spark plugs, all fluids changed, battery, and even upgraded the wimpy stock horn to dual Hella trumpets.

Maybe it is the Cats?