Check Engine Light, VCS Light - P0420

quick fixes for this one?

 

here's what the mechanic said.

 

V8 or V6?

I recently had this issue on my V8 and replaced just the O2 sensor. Driver side in the case of the V8. V6 I think is actually passenger side for the P0420.

Code came back once as a pending code. I then replaced the exhaust gaskets for the y-pipe/crossover pipe, which is after the cats, and the code has not come back since.

Just my experience, not saying it will fix your problem but it's the cheaper route to start with IMO.