Can we talk about the guy at the parts counter who said you can't fix a P0420 code without a new cat?

I was at the NAPA in Bellingham yesterday and overheard a young tech being told a P0420 on his 2008 Civic always means the catalytic converter is shot and needs a $900 replacement. In my experience, that's just lazy. I've cleared that exact code three times this year by fixing an exhaust leak before the O2 sensor or swapping a bad upstream sensor first. Has anyone else had luck with a specific diagnostic routine for P0420s before jumping to the cat?

4 comments

4 Comments

dylanwells3mo ago

Man, my buddy's truck had that code and it was just a cheap O2 sensor.

johnson.eva3mo ago

Cheap sensors cause expensive problems.

the_riley3mo ago

So what's your actual diagnostic order for checking everything else first?

dylan_ward17d ago

Used to be the guy who'd swap parts first until a buddy proved me wrong about a MAF sensor that looked clean. @dylanwells kinda hammered that home with the O2 sensor thing too.