Return of P0420 code?
Please note, I'm not car savvy, including lingo, nor can I really fix stuff myself when it comes to cars. So keep that in mind!
2008 Volvo S40 with 219,816 miles. Beginning in 07/2020, I began having a check engine light come on and off that was identified to be code P0420. In 03/2021, I finally got it fixed when my local mechanic replaced our catalytic converter. Looking at that invoice, they also replaced the exhaust gasket, upstream and downstream oxygen sensors and replaced spark plugs.
Fast forward to now. On 2/10/23, my wife mentioned our check engine light came on and it's still on as of this message. This past 2/14/23, I took it to Autozone to get the code read and he said it showed code P0420. The rep there asked if we got gas recently and I told him yes, my wife got it the previous day on 2/9/23. He recommended simply changing out the gas cap to fix the problem. This is interesting to me because all that time from 7/2020 - 03/2021 when I finally replaced the CAT, I had always suspected and wondered if it was simply a gas cap issue. But I read information online with others shooting this idea down and say it would show a different code for that, etc. Is this simply an easy fix with the gas cap since we just replaced the CAT, etc. just two years ago? But even if it is just the gas cap, did I replace the CAT, etc. for no reason at all? My wife has mentioned the car doesn't feel any different driving since the light came on, from the best she can tell.
If this has nothing to do with the gas cap, I'm so lost and have no idea how to fix this problem. So confused and frustrated.
Thanks in advance for any help you can give.