Thread: CAT or O2 Sensor

Hey Guys,

my 01 GT is throwing a PO420 code. Can't seem to figure out if it's the CAT or O2. Car has been running a little sluggish with poor fuel mileage.

Any thoughts?

Thanks

T

Someone had this code on here just recently. And is the first time I have ever heard of this. They said they changed out the o2 sensor and it went away. I think it will be back though.



I have never seen an o2 sensor code that said catalist system low effeciency. And have seen a lot of o2 sensor codes.


I think you're cat is getting clogged and you may need a new one soon. And that is also why it is sluggish and you are getting poor fuel economy. That o2 sensor does not do anything with fueling in the car. It is only there to see if the cat is working properly. THAT IS IT!

And that's what is is doing now.

Originally Posted by Sabrewings

I've seen this a lot. Especially when I worked for a dealer. The O2 sensor goes bad but not to the point that it trips its own code. It shows false readings that makes the PCM think the cat is bad.

If he has a stock cat, it's the O2 sensor.

Do you think that it is actually the 02 going out more of the time than it actually being a bad cat? Especially seeing that these cars usually have a pretty good amount of miles on them? Good info non the less.

Thanks guys

Originally Posted by Scimmia

Are you running a stock cat? If not, many aftermarket cats throw this code all of the time, they just don't work as well as OEM.

If you are stock, hopefully you're under 120,000 mi, because GM extended the warranty on the cat on the 01-02 L36 because of a defect that could block it. Take it to the dealership for a free fix.

Awesome info about the recal. Did not know that myself. And good paint about the high flow cat's.