Hi Every1
I've got recurring codes


P0420, Replaced complete Exhaust with Magnflow. P0420 back again in 6 months, replaced Cat Conv under warranty, Now its back again and my mech says aftermarket Cat Conv is no good. Say I need original GM Cat.
And thoughts on this?


P0455, Evap, Large Leak. Last time he replaced some sort of canister that's near the gas tank, I wish I paid attention, but that was 3 months ago and now P0455 is back. Says it could be lots of things, he's going to do a smoke test next week when in in for other things, steering rack, but that's another issue...


And body got experience with these things?

 

Very common for aftermarket cats to give that code. The original spec has low tolerance for change, I would honestly just recommend getting a tune and removing the code completely.

If you can't find the EVAP leak, the smoke test is the best bet. There are so many little rubber lines and small areas for a leak.