2009 Chevy HHR with 82,000 miles. P0420 Catalyst below threshold.

Just wondering the best diagnostic steps before assuming the Catalytic converter is bad?

Robert

 

Great tips in this link.

https://www.obd-codes.com/p0420

 

Start looking for a new cat. Look on eBay.

 

https://mufflerexpress.ca/products/c...-2-2l-and-2-4l

Not too expensive

 

And fix whatever caused the failure.
Usually caused by misfires or running too rich. If the cat gets too hot the catalyst melts. Sometimes somebody used silicone that got into the combustion product, that contaminates the catalyst. Sometimes burning oil introduces contaminants, "high mileage" formula oils are worst.

 

And let’s not forget the icky coolant leak, it killed a cat on my 2007 LS

 

Thanks for the input on this. I've dealt with this on another vehicle before and I learned it's not always the Cat that's bad. It really sucks to install Catalytic Converter only to have it not fix your problem. Of course odds are that the Cat needs replaced. Anyways, I've scanned my O2 sensors and they seem to be working ok. Looks like the best course of action is to check the spark plugs, exhaust leaks and fuel injectors. Did I miss anything?

Robert

 

Are there any other codes? Any recent work or issues? New O2 sensors, in particular? Is it the original cat? Any evidence of exhaust leaks in the area of the cats?

Does the car make a lot of short trips?

It's a pretty sure bet that tha cat isn't up to par, but that doesn't mean you should run out and by a cat. In particular, if it's the original, it should be preserved if possible. It may be possible to take a nice 1-2 hour freeway drive an burn off a mildly gunked-up cat. But not if there are other problems.

 

Spark plugs, AC Delco 41-103 iridium ?
exhaust leaks at the manifold or flex pipe?

dirt and crud built up around injectors insulators?

 

Bosch O2 sensors have caused problems. Use NGK/NTK if you need to replace what's on the car.