I have a 2008 H3 Alpha with 122,000 miles on it. I get a code P0420 about every 100 miles or so. Catalytic converter inefficient bank 1. Started getting this after I changed out the bank one O2 sensor 1. I moved all the sensors from bank 1 to bank two and visa versa. Figured if issue moved it would point to a bad sensor. Issued stayed on bank 1. Guess I have a weak catalytic converter. Always used tier 1 fuel. Can anybody recommend a good catalytic converter that wont break the bank and do I have to replace both sides? If somebody has a trick to clean the catalytic converter I would be willing to try that or if you think I am stuck changing the converter out that is what I will do. Thank you

 

You can't clean a worn internally failing catalytic converter. In the meantime just install a set of spark plug non-foulers.

 

Put an extender (stand-off) on the secondary sensor.

 

I have the exact same issue; '08 Alpha with 145,000 miles. In CA, I have to replace with an OEM cat, no aftermarket allowed.

 

I just find it odd that I can clear the code and it doesn't come back for maybe a couple hundred miles. I would think if the cat was inefficient the code would come back fairly shortly after driving again.

 

That's how mine is; sometimes I can go several weeks, other times it will trip the code every other day. Seems to be getting worse lately. Drives me nuts, and I'm getting ready to smog it, so I need to time it just right!!!

 

Extend the cat monitor 02 sensor (down stream sensor, behind the cat)

Many how to videos on YT.

 

Like I said!

 

Thank you all for suggesting this! Mine had gotten to the point where it would simply not complete the drive cycle without throwing the P0420 code. I swapped the downstream O2 sensors from right to left and vice versa, hoping that it would follow the swap (P0430 instead), but it didn't. So I decided to give the anti-foulers a try, since I needed to get the truck smogged. Bingo! It worked! That buys me at least another 2 years before I have to address a $1000 catalytic converter!

 

Actually you should be careful with the "Used Car Salesman" repairs. You can do damage to an otherwise fine motor when faking the PCM to not monitor CAT efficiency so that you will not know how bad it gets. Ever see people driving with their exhaust glowing red, car smoking, clueless to their problem?