VSC OFF and P0420 Issue

I recently purchased a 04' 4runner with 111k miles. The 4runner has an aftermarket spotlight and I had turned them on and I noticed a check engine light + VSC off light appear. So I return home and run my OBD2 scanner. I get the P0420 error which is a catalytic/O2 sensor failure. So I cleared the codes and the VSC light turned off along with the check engine light. Now I am going to replace my Bank 1 O2 sensor, but I'm still confused. Could my spotlight have caused the O2 sensor to stop working and disable my VSC?

 

VSC light will always come on when you have a CEL.

I think when turning the light on and you get the CEL was a coincidence

 

You could replace your downstream sensor(s) and see if that resolves the issue. Personally, if the sensors have more than 100k miles on them, they should all be replaced. Use Denso or OEM sensors for the replacement. After that, you need to have the condition of the cat(s) checked out. If your OBD2 reader is capable of running diagnostic tests, you can do it yourself. Many times the cats get extra build up and can be cleaned. There are other times where the cat is damaged beyond repair. Other tests you need to consider is to check the fuel trim, leak check the exhaust manifolds, and condition of the spark plugs. There are many factors involved when diagnosing a cat code. You need to ask yourself, why did the cat go bad, before replacing it, because if you don't resolve the issue, the new cat may go bad as well.