So do I buy a new O2 sensor for the bank 1 code or put in a new catalytic converter?

 

do you have any loss in power? a rotten egg smelling exhaust?

 

This may help:
P0420 DTC Code - Catalyst System Efficiency Below Threshold (Bank 1)

 

I did have loss of power with prev code. Changed plugs and coils. Cleared first code and loss of power. Press right pedal and it goes like it should but PO420 persists. The link shows lots of questions but no 'answers'. Most remedies would be ones I would chase, replace cat and O2 sensor but they state this rarely solve prob. Only two remedies actually different. Gas with no ethanol and a pcv valve change. Woe is me! What to do?

 

The PCM is complaining about the cat. So it could only be the cat or the downstream O2 sensor, including the wiring associated with it. Most likely the cat is no longer cleaning the exhaust and has to be changed. With a scanner compare the activity of the upstream O2 with that of the downstream O2. The upstream O2 should be changing value at a rapid rate, the downstream O2 should show a steady voltage. If the downstream O2 is changing voltage at about the same rate as the upstream O2, it is an indication that the cat has failed and not cleaning the exhaust.
It seems that you are looking for someone to tell you exactly what has to be changed, but without proper testing, all you are going to get is a SWAG.

 

It would be best if someone could say that I would be grateful however I know better. Looking at all the info it seems like the solution has expensive pathways. I see remedies like r/r O2 and r/r catalytic. One post indicated a non-ethanol fuel. I hate to admit this but in my field there are service techs can perform work with pricey added tasks which are useful but not needed just to pad a invoice. I had one mechanic tell me lets do a tune-up, oil change, fuel injector service and hope that fixes the problem but 'it might not'. Being a diy guy I can't afford the padded costs because the tech needs a big paycheck. I have found value here which tells me this forum can offer true and affordable advice. So this forum looks to be full of honest approaches. Finally, I usually work on the task check and clear the code with the OBD reader from the parts house. If I did not solve the issue, the code would return after so many miles. What does disconnecting the battery achieve regarding resetting the codes?
Thanks for your time

 

This code is 99% accurate if there is no O2 codes that are with it. Your cat will start losing effeciency well before your car loses power. Waiting until the CAT plugs up will cause more damage to the engine so replace it sooner than later. Also replace the downstream O2 sensor when the cat gets replaced as this is the sensor that monitors the cat's health. I myself am a DIY tech and a former GM mechanic. I also know the 3.8L engine better than any of the other engines that were put in these cars. For you if you are going to do this yourself you may just want to get the exact fit cat from your favorite part's store. If you have access to welding equipment then you could go with a universal cat. Here in my neck of the woods we have a performance exhaust shop that will install a high flow cat with quality workmanship for the same price as the exact fit one from the O'Reilly's I work at. You may want to see if there is an exhaust specialty shop near you that can hook you up. Also ask the part stores in your area who they would recomend. If you keep hearing the same shop name it is prolly a good shop.

Massey

 

With OBDII computer systems the computer does not forget codes after the battery has been disconnected. It will store the codes in memory. You have 2 options. One use a scanner to clear the codes, or wait until the computer has decided you have fixed the issue. Using a scanner will put the computer's test cycles all back to 0 which will cause the computer to systematicly test all systems in the car. This may take a few days for a full run and you may have to wait a few days to see if you actually fixed it all. Letting the computer turn it's own CEL light off will take longer, possibly a few weeks.

Massey

 

When I had my 2001 3.8l I got that code the day after I picked it up. Called up the dealer and they installed a new cat. Never had the code come back until I re did the whole exhaust system with headers, etc.
So if it's stock exhaust I agree with the others that say new cat is the way to go. As Massey said you can get universal pretty cheap. If I remember correctly when I re did the exhaust I got a universal 3" In/Out high flow on eBay for like $65 shipped.

 

Massey, thx for your service.
Will look to have cat and O2 changed.