Hey guys, I know this has probably been done before, looks like a fairly common problem. But I'm on my phone at the moment at work and couldn't find a good plan of attack for getting rid of the code.

My reader says P0420: Catalyst system efficiency below threshold (bank 1).

Would my best bet be to replace the downstream O2 sensor first? Then possibly my cat if it doesn't go away?

I cleared the code the first couple times and it went away for a week or so. Cleared it last night and it came back this morning.

Thanks in advance!

 

yeah the one after the cat cause thats the one telling the computer the cat isnt doing its job. weve done this at work a few times for people who didnt want to put any money into their vehicle but the light always came back. 98% of the time replacing the cat fixes the code

 

99.9999% of the time its the cat. forget the sensor.

 

Gotcha. I've been wanting to run dual exhaust for a while now. Now I have an excuse to do it, I'll just throw a high flow cat on when I do it.

Good to have some confirmation that's the problem!

When I get it PCM tuned in the future I'll delete that rear sensor too in case the high flow throws it.