P0420 after long-term storage

[pearlwhiteprojects163]

Okay, so the car's been chilling for a year, right? Got it running after swapping the battery and fluids, but now it's spitting out a P0420 code. The O2 sensors seem okay, but that code pops back up after the CAT monitor does its thing. Think the CAT went bad just from sitting around?

 

[Kayleb]

It's possible, sitting for that long, especially if moisture got into the exhaust, can cause the catalytic converter to break down or get contaminated and even if the O2 sensors are reading fine, the CAT might not be doing its job efficiently anymore, try running a good-quality fuel system cleaner and putting a few solid heat cycles on it, but if the code keeps coming back, odds are the CAT's on its way out already, sorry boss

 

[brutalheir06]

Check for any small exhaust leaks upstream first, my best guess but if not I'd have to agree with @Kayleb about the CAT being on its way out