so this has been going on for about two months now.my check engine light will come on for a few days the tunr off.its really starting to **** me off.i went to the dealer to day and they cant look at it till tuesday morning. did vechile scan and this code came up P0420 Catalyst Efficiency Below Threshold,cansome one tell me what it means and how i can fix it.

 

are you running a non-catted downpipe?

 

no i am not.i also notice that the check light only goes on when im at littel less than half tank.when i fill up it goes off.i think i got bad gas a while back.

 

could be your gas cap, when you screw it on, you make sure to keep turn until you hear it click like 5 times right?

 

When I was catted, I had two episodes with that problem. The both times the dealer reset the code first and sent me home. The code popped back up within a few days typically. They then replaced the O2 sensor and sent me home. Again, the code came back. Then they replaced the catalytic convertors. Viola, the code went away. If I had no warrantee, the cats would have cost me in the neighborhood of $500 as I recall. Now I am catless and my *almost new stock catback system sits in the shop wrapped in plastic!

 

I had the same issue. But now I have it come and go all the time. I checked it and I forgot the code but I thought it said something along the lines of a bad O2 sensor. I need to check it again. I will then post up the real code#. I am catless all the way so I think thats where its coming from. But I installed a Perrin CEL fix, and I am still getting a CEL. I too could use some help.

 

I tighten my gas cap till a clickslike 5 times i beleve the coed says the the cat effiency is below tresh hold.