Yesterday I posted something kind of like this in the lsj section but after doing some research I don't think my o2 sensor is the problem so this section seems more appropriate.

I have a p0420 code which I understand usually happens after installing a high flow cat.
My car has stock exhaust and is throwing that code...it also get's terrible mpg's compared to what these usually get (21 city, 27 hwy), is this one of my o2 sensors? I'm totally lost as to what exactly could be wrong.

please help

 

are you on a gm tune or not? stock exhaust (header , DP, and catback)???

 

Clogged Cat?

 

The stock gm one, I'm not on a stage tune or anything, literally everything is stock on the whole car except for the air box mod

It has 69K miles so i doubt it, but I have no idea

 

You would be surprised. lol my buddies clogged at 40something. His symtoms were cel, poor gas mileage and loss in power. He is now catless.

 

The same cel I have?

That would be a relatively easy fix because I could just switch to a zzp catted downpipe

 

Im not sure it happened a few years ago I cant remember. Hopefully more people chime in that can help. You would experience a loss in power to though if it was clogged.

 

I've only had the car for 2 weeks but it doesn't feel like a slouch so maybe that isn't the problem :/ Even though I probably will try it if I can't figure anything else out.

bump for any more input!

 

Best thing to do is get someone with a scope and a QUALITY scan tool that can read freeze frame and be able to watch your O2 voltages and O2 waveforms and look at the reading for the 2 sensors.

If you do have an issue with the O2s/cat(verified by diagnosing not part slapping); I would Highly recommend replacing both O2 sensors and the catalytic converter.

90% of the time; cat and O2s will take care of it. And while your in there putting in your new header and catted downpipe; go ahead and clean your throttle body, drop down a couple pulley sizes, throw some bigger injectors at her, some cooling mods, and finish her off with a fresh HPtune.

 

where can i get a good scan like that at? i really wish all that stuff was in the budget but it looks like for now i just need to get everything running as it should. :/


Posted from Cobaltss.net App for Android

 

Most reputable shops use eother the factory scan tools or use the snapon solus (pro)
More than likely you will have to pay a diagnostic charge starting at an hour; My shop is 114.95 per hour

You could get the shop to do the diagnostic and you fix it yourself. If they charge you more than an hour to diagnose that, unless there is something seriously screwed up, It should only take them 20minutes to verify that you need cat and O2s...

Via the interwebz diagnostic; I would put money down that you need cat and O2s. If you do spend the money and get a zzp/ottp/badmab/ect. quality header and/or downpipe; You could possibly set the code again due to high flow characteristics of the cat. Then you delete the code with your tuning software of choice, and your good to go

 

Oh; and if you purchase these parts...Get ACDelco O2 sensors; Aftermarket sensors WILL NOT be accurate; I have gotten several cars in the shop that have had shitty afromarket sensors put on just to save a few bucks and they end up shelling out more money to have it fixed right the second time around.

 

Thank you for your help! Do you happen to know the ac delco part numbers for the sensors? I always come up with an unending list of different numbers when I try and find them lol

 

Check with muffler shops. They can tell if the cat us clogged by screwing a gauge into the o2 sensor location.