So I have an 08 dodge avenger, here's the problem my check engine light is throwing a P0420 bank 1. So accordingly I changed both sensors and my catalyst yet still the same code still is being thrown. The numbers on the parameters are good when the sensors are talking to each other yet they keep reading low at the same time and high at the same time. What should I do next I am so confused.

 

I have the same exact problem (only bank 2). The cats, o2sensors, spark plugs, coils, throttle body and much more has been changed. Vacuum leaks and exhaust leaks have been tested. I'm out of my wits here. Does anyone have any ideas what might be wrong?

 

Seems to be a common problem. I have the P0420 (bank 2) code and took it my mechanic. He tested the 02 sensors and they are working fine. It's not a compression issue (gas cap) either. He dug further and told me the 1 cat was not good any more. I have the 2.7L engine, only 127,000 kms on it - all city driving mostly. I've even tried a quick "guaranteed to pass your e-test/shut off CEL" trick that seems to work from YouTube where the rear O2 sensor is backed off with a spacer - didn't work in this case! After the drive cycle, it's back on. Was going to try this temporarily and see if it solved the problem.

Does the 2008 Avenger SXT have 2 cats? If I am remembering what he told me correctly, there is a L and R cat on this car? He said the one was fine, but the other needed replacement.

Also....he also told me this - He is leery about changing the 1 (my cost over $1000.00 CDN), because I'd then have a new and original, and the sensors may not get proper readings, thus resulting in it still throwing a code.

I am hoping this is not an all too common issue with this car. I have had my CEL on for a while now, but it runs fine. I can't even bother thinking about a getting my e-test done, as a CEL ON is automatic fail.

 

Look up under it and you can see if it has one or two converters.

 

Yes, it has two cats. I got mine sorted. It was the cat that has gone bad. Do not buy a used cat, it won't work even if the used cat was good. In my car we tried two different used cats with no luck. Only when I had a new cat did the cel stay away. I had luck and the dealer whom I bought the car payed all the repairs but the new cat was well over 1000€ with labor for them.