Is this something I can fix myself? I can do many car repairs but I’m no expert.
Some are bolted in, some are welded solid to your exhaust system. This is a common problem on Jeep wranglers, they have 4 cats, two on each side. It has only two O2 sensors oddly though, so the second of cats are not monitored whatsoever. All four are welded in and so it's a cut and weld job, or buy the whole new apparatus for $300-$900 depended on where you buy. Not sure how your Buick is set up.
They are bolted directly to the exhaust manifold, so you would need to work from underneath the vehicle. If it's an AWD it starts getting difficult because the transfer case would need to be removed, otherwise there is a sub frame brace/cross member and the exhaust pipe/y-pipe that needs to be removed. I don't know your level of experience but FWD is not too difficult, AWD models are fairly difficult. If the exhaust is rusty or corroded then the difficulty goes up if you have to deal with broken nuts/bolts.
When I have a car like that 180,000 miles and code or engine light comes on I do as you and research it.
I also monitor the MPG and see how it drives..If it gets the same MPG I do not worry about it.
My 1995 corolla emission code came up and this was at 150,000 or so miles.
I checked many things and decided it still gets 33.5 MPG so told the wife keep driving it and I put a smiley face sticker over the light.
Eventually the light burned out and the sticker fell off, still gets low 30's MPG and has 322,000 miles on it.
It sees full throttle every time I drive it.
Oil changes at 3000 miles trans fluid changes at 6000 miles and antifreeze at 50,000 miles, timing belts at 90,000.
Car washed under the hood and undercarriage every oil change.
We check MPG on every fill up on our cars.
Monitor it and drive it.
I also monitor the MPG and see how it drives..If it gets the same MPG I do not worry about it.
My 1995 corolla emission code came up and this was at 150,000 or so miles.
I checked many things and decided it still gets 33.5 MPG so told the wife keep driving it and I put a smiley face sticker over the light.
Eventually the light burned out and the sticker fell off, still gets low 30's MPG and has 322,000 miles on it.
It sees full throttle every time I drive it.
Oil changes at 3000 miles trans fluid changes at 6000 miles and antifreeze at 50,000 miles, timing belts at 90,000.
Car washed under the hood and undercarriage every oil change.
We check MPG on every fill up on our cars.
Monitor it and drive it.
I actually saw a video on YouTube and I can change it myself. Mine is FWD. My only issue is if I change that cat and the other one is bad. I don’t see any videos changing the other one. I can say this, it seems to drive the same but I don’t drive it very often. I did however smell an exhaust smell at the front of the vehicle that I have never smelt before. And when it idles it seems to idle up and down. Do you think I should have my mechanic look at it or do you think I should just order the new cat and change it myself? I told him what the code was and he said it could be numerous different things. A bad cat being one.
How much are you willing to spend to be wrong over and over and over compared to a mechanic?
O2 sensor
O2 sensor
If you have a plugged cat, you should notice a performance difference, especially at higher rpms with quick acceleration. It should feel doggy and often times they will cause a misfire even. O2 sensors don't cost much in comparison.
Does it have a fuel filter? If so, when was it last changed? If it has been a bit, change it.
The biggest concern is, what if anything might have caused the failure, they do go bad with age but excessive fuel is a major killer. If the engine is running rich, or misfiring this can cause the failure, though you will usually have codes pertaining to those concerns too. With the year and mileage of the vehicle it could simply be degraded enough to set the P0420 code. If the other side fails, you will get a P0430 code.
Back before OBII, without analyzing a vehicles exhaust emissions (smog check), there was no way to know if the catalytic converter has failed on efficiency. OBDII does this now by comparing sensor values before and after the catalyst. This is not the same failure as being clogged or restricted, which would cause a noticeable reduction of power. Modern vehicles can still get clogged converters but most of the time they fail is with catalyst efficiency, they can flow fine, just not cleaning the exhaust up.
Back before OBII, without analyzing a vehicles exhaust emissions (smog check), there was no way to know if the catalytic converter has failed on efficiency. OBDII does this now by comparing sensor values before and after the catalyst. This is not the same failure as being clogged or restricted, which would cause a noticeable reduction of power. Modern vehicles can still get clogged converters but most of the time they fail is with catalyst efficiency, they can flow fine, just not cleaning the exhaust up.
