P420 code that won't go away.

[LoveMy02W68]

My check engine light keeps going on and my ODB2 scanner gives me the code P420 which says "catalyst below efficiency". My downstream 02 sensor was changed a few days ago and the upstream ones i changed at the end of the fall last year before I put the car away for the winter.

My guess is that it's running lean. It's supercharged with the PCV mod in the throttle body, valve cover breather, 6:1(i think?) FMU. Pacesetter headers to a full magnaflow exhaust.

The car runs fine, it's just the stupid emissions is giving me a hard time. And I haven't been able to drive it because my inspection is up and it won't pass. Any ideas on how to fix this or at least get around it?

[97rs4life]

Re: P420 code that won't go away.

well is it the stock cat or aftermarket cat? That could is for a faulty converter so even swapping the o2s isn't going to change anything. We need more info ;)

[bwkmaro]

Re: P420 code that won't go away.

hptuners and make it go away forever

[whitdog54]

Re: P420 code that won't go away.

Assuming you have pacesetters and magnaflow exhaust....you must have hi-flow cat. Since its flowing more then stock you are going to throw that code.

[LoveMy02W68]

Re: P420 code that won't go away.

full magnaflow exhaust = hi-flow magnaflow cat too.

The only reason I changed the o2 sensor is because that is whats sending info from my cat to my computer, so i figured maybe it's bad? But i guess thats not the case.

I want to get it to stop throwing that code, and what do you mean hptuners make it go away forever?

**Also, I was looking at o2 simulators. Any opinions? I'm not sure if they're gonna stick that wand thing up my tail pipe, it's an 02 and I know there are certain years they do/don't test like that.

[whitdog54]

Re: P420 code that won't go away.

Well on the internet full magnaflow exhaust DOES NOT mean you have a magnaflow cat...most people would perceive that as having an aftermarket s and i pipe.

hptuners is a tuning software. You can just tune the code out...forever. Or just live with it. Mine goes off and doesnt change MPG or performance one bit.

[97rs4life]

Re: P420 code that won't go away.

hptuners or an o2 sim will eliminate the code. the hi-flow cat is causing it, not the sensors themselves

[cam98aro]

Re: P420 code that won't go away.

if you are too cheap to get hptuners, you can buy an o2 bung and move the sensor back, it should take care of the code

[whitdog54]

Re: P420 code that won't go away.

if you are too cheap to get hptuners, you can buy an o2 bung and move the sensor back, it should take care of the code

hmmm never thought of that haha. May consider it.

[LoveMy02W68]

Re: P420 code that won't go away.

if you are too cheap to get hptuners, you can buy an o2 bung and move the sensor back, it should take care of the code

Well I gotta tell ya, it works wonders:excited:

Thanks for the input guys, problem solved (for now anyways)