Hello, we have a problem, that i cant figure why is that happens.
i have a Chevy Malibu 2015 with LTG engine.
i have a custom exhaust with High-Flow 3" Downpipe with 200 Cell Magnaflow Cat.
when the tune that i use is loaded there is no P0420 Code is appearing ( DTC reports not touched in a tune ), when i load a stock tune, the P0420 is coming after about 70km of highway cruising.
i want to understand why the thing is happening and if this is dangerous.
one thing that i think about is that somehow the AFR is messing and its get LEAN burn and Exhaust temp get up and heats up the cat and its burns things "better" hope i"m wrong.
i"m attaching stock and my tune file ( based on ATS diablo tune ).