P0420 Bank 1 question

[Wydz]

CEL came on last night. Went to O’Reilly’s today and it shot out the classic P0420 code under Bank 1

2014 Sonic LT 1.8L 41.5k miles completely stock except a Kn air filter

Now my points are:

Nothing sounds different at all I’ve notice in my exhaust system setup
No idle differences or idle knocking.
No power differences or weaknesses.
Car doesn’t drive differently at all that I’ve noticed.

My car starts normally fine but my key fob remote start won’t start the car yet everything else works on the key fob.

I know this gets posted a lot I just want to know where to start if it’s something I could do myself with help of my neighbor.

 

[OssiansFolly]

I have to ask, did you change your spark plugs/coil lately? My ex needed new plugs and when I changed them out this code came up shortly after (this code is what prompted me to change the coil/plugs). I bought nice plugs and a new coil, so it shouldn't have failed. A buddy who is a mechanic suggested that using platinum plugs will cause this and I should stick to OEM equivalent plugs. Sure enough making that simple change fixed it. The car ran fine, so I only started trouble shooting when the CEL came on. She has a 2012 Sonic.

That being said, one of the easiest things to check is going to be the plugs and coil. You can easily open that up, look for burns/marks, and put that back in under an hour.