so im getting p0420 thrown on my dash. ive replaced Both o2 sensors already and my maf sensor. i dunno what could be causing this. if my cat was clogged i wouldnt be able to build any rpms correct? occaisionaly it will throw the code for my rear o2 sensor too. and for about a month it was having alot of trouble starting when the motor was cold. it would flood the motor. anyone else come across this problem in their journeys??

420 isn't that the Smoke a fatty and your problems go away code?

tried that but it only made me hungry. it didnt turn off the light LOL

If you have modified your pulley, and generate more boost, you will get the 420 if you have not tuned your PCM. If nothing has changed, then you are in the same boat as me...random show up of the 420.

I can almost guarantee if you have a 2001/2002, your Cat has begun collapsing inside, and the end result is the rear O2 reads funky, throwing the code. There is a TSB for this somewhere in the database.

I have not had mine in just yet, but others I know have experienced this on the older models. I have to get emmissions testing this month, so I will know my cause very soon. I'd get your Cat checked.

If for some reason you are really finding the flooding, and overfuelling, it could be a messed up MAF sensor. If you overfuel, your O2 will get coated quickly with residue and give false readings. If you have changed it, are you running a KN Filter, and did you possibly over oil it?

Damm i was sure that would work

I do have a k&n oil filter on it but i have not cleaned it for a while (speaking of wich i think i will this weekend) and i did replace my MAF in the summer. its a really wierd problem. got me stumped. I heard the only way you can have a cat tested is to actually take it off the car and visually inspect it. if im gonna do that i may as well just replace it. I kinda dont wanna throw any more money into the car though because im wanting to sell it.

I've been out of Alberta for far too long...the 420 out here don't even make me hungry...

I'm not sure the testing technique, but I believe the right emissions testing guy can determine the condition. Then again, you don't have any need for testing yet, so those guys are probably far and few between in AB.

If you havent cleaned and oiled your air filter in a while, maybe it is letting dirt by affecting your MAF. KN needs oil to stop dirt.

When I did my headers and high flow cat, allmost right off the bat I started getting the 420 code , kinda annoying, when I get some cash and have a chance to get a "Will" tuned pcm , I will get him to remove that code.

Once you increase flow, you will have to delete it.

well whatever it was, its fixed itself... it is not doing anything anymore it seems to be running fine and not throwing any codes. im almost wondering if some water just got in a sensor plug and caused it to throw the code. we did have it pretty wet for a while after i changed my sensors, then it froze up. probably froze water in it.

Now thats why I love GP's they fix themselves

so i spoke too soon. it threw the p0137 code this time though.... AARGH fricken gm cars.