2020 RS3 P0420 with 14k miles?

[Divine_elegy]

Hello,

I recently bought a 2020 RS3 about a month ago. It threw a CEL (P0420) which is weird because the car has 14k miles. It was tuned, but got flashed back to stock before I bought it. The P0420 code indicates that the cats may need to be replaced.

Took it to an Audi dealership and told me theres nothing they can do because the car was modded before (TD1). I took it to the dealership I bought it from and they’re telling me that they performed tests on the cats and everything seems fine.

My question is can the cats actually go bad after 14k miles? Before taking it in, I did some testing on the upstream/downstream live data and everything seemed fine. I even cleared the codes and drove a bit. After a couple days, light came back on.

The car also appears to have a stock downpipe (ive read aftermarket downpipes will throw a P0420) and has a catback exhaust from IE. I dont think that would cause the P0420 since its a catback setup.

Does anyone here have any ideas as to what the heck might be going on?

Thanks!!

[MikTip]

It could be a bad o2 sensor...

[Divine_elegy]

Both places told me sensors were fine

[MikTip]

So it has an IE exhaust...can you verify the down pipe is OE and not IE?

Heres my experience.. I had the same thing happen to my Audi running a custom down pipe 200cell cat with OE rear sensor after installing the OE down pipe.

Once the sensor was replaced with a new uncontaminated sensor, everything was fine.