My car is throwing a P0420 code. Which would be more likely to cause it, the oxygen sensor or the cat? I currently have a dp from Clear Image with a high flow cat. Any help would be great.

 

I had this too, I think it's from the high flow cat.

 

I have the same code but i'm under pressure because my emissions is due next week. I have the GMPP Sport exhaust and the factory cat...

 

Yeah I have vibrant header/downpipe combo, but for some reason it just went away the other day...no longer have the code

 

ok a p0420 means the 02 sensor is not showing the change in milli volts like it should which in return means your cat is plugged, or not doing its job or the 02 sensor is at fault....... A good thing to do if your car gets the p0420 is take there rear 02 out, and clean it with high heat like a torch. Install it,if the 02 sensor was bad from carbon bildup i would have to say that the torch would be a quick fix but not a long term fix. Also usually when the p0420 code comes its a cat not the 02 sensor, so look there first, check for rattling, and a bad exaust pressure.

 

lmao! @ allgood i got the same combo and it comes and goes!? hey when you installed the header and dp, did your o2 sensor for the dp reach? mine didn :/

 

so if its a catless dp would that same code pop up??

 

yes you will get a p0420 since the rear 02 sensor will be reading millivolts that it shouldnt, it would be like a front 02 that is supposed to change drastically in milli volts to keep a afr of 14.669 and the rear 02 should stay a constat millivolt because its just tere to check to see if the cat is working

 

yikes... I just drive the car and take care of the routine maintenance... So i'm unsure how I can check for the exhaust pressure. Is it hard to have someone change out the rear o2 sensor? I really don't want to pay the 700 for the cat... Maybe I should just get a high flow one?

 

I've got this code many times with my high flow cat. It happens mostly driving around town especially when the weather is colder. The cat doesn't get hot enough to work properly. The high flow cats barely do enough on a good day to not trip a CEL.

With my dashawk its a breeze to clear the code though!

 

so what high flow cat do you guys recommend with my set up?

 

Well, I temporarily fixed this on my car. I did the ol' spark plug non fouler trick, and so far so good. I would clear the code before, and it would come on within 15 minutes. I drove around for 30 mins or so, and it's still off. I have to pass emissions by Monday, if not I can't renew my registration, so hopefully this solved it for me. Those having trouble with the same code should give it a shot, $4 and an hour of time should hopefully solve it.

 

You better get a lot of drive cycles in there to pass.

 

I know, my code reader has monitor status read outs as well, so I know when I'm ready to take it in. I'll be driving most of the day tomorrow just to set them.