So I know a lot of you have posted about this code and posted what could be wrong, but I got a new zzp down pipe with a cat a month ago and got a p0420 and a lean code yesterday...anyone run into this or similar with a new cat

and that dp is all I have done to the car

 

Yeah its because your running a highflow cat now and the o2 readings are off and the ecu is giving a code because of it. You got a few options you can either ignore it or get your car tuned which is what I did. I would wait until you get a few more performance mods like cat back exhaust ,intake and smaller pulley if your supercharged etc that way you'll get the maximum benefits from the tune. For a tuner your best options is hp tuners. See if someone local in your area has it and then go to them for a custom dyno tune.

 

@Monieg5gt thanks

 

p0420 is the catalytic efficiency code like Monieg5gt explained above just stating cat performance isn't sufficient which won't affect drivability for LSJ or base model cars. Idk about LNF turbo Cobalts as they seem to do a lot of that stuff differently than what I have experience with in supercharged application. On the other hand the lean code is concerning and should not be ignored. I'm not sure if the downpipe can allow enough additional airflow to cause a lean condition by itself or not but I'm assuming you never had your tune adjusted?

 

@jdbaugh1 no I’ve never had it tuned..I have a 07 lsj and I did all the things to try and find a vacuum leak (not saying there still couldn’t b one) but nothing cleaned maf sensor 3x ran fuel injector cleaner thru and checked to see if they were working..all checked out....the lean code came on before the cat code so I was fighting with that and now I have both

 

The lean code more than likely is affiliated with the high flow cat. Two things are happening, more oxygen is being measured in the downstream o2 and you open up the breathing a lil more. You can try an 02 sensor spacer in the downstream but that's kinda the ghetto way, a tune is a much better fix and the pcm with be getting the true readings so you get the proper fuel trims

 

See if you can find someone or just buy a $20 bluetooth OBD II reader and monitor the fuel trims to see when the lean condition is present.