[neilvan]

So Ive had my 2.5" catted Downpipes on my 335 e90 for a few months now. Even though the code comes up less I still get a P0420/P0430 code for rear O2 inefficiency.

Now I know the cats are smaller than stock blah blah blah. I was wondering how many other people get these codes with catted downpipes of if the cats are toast.

What catted pipes specifically?

This is typically why peeps just go catless to begin with...most aftermarket catted pipes will eventually throw codes; mostly depends on brand/quality of cat. I think older DME/ROM versions weren't as picky, from what I recall, so fewer issues with those cars.

[neilvan]

Not sure on brand of downpipes. I bought them used. PO apparently only used them for a year.

Judging by the markings on the cat, they are Vibrant units. Ones I have used before with no issues on modded cars.

Car is an 09 335. I have a race car and this is my daily which is why I wanted cats. Have a bi-ennial emissions test which is just an OBD plug in.

[JuniorB]

Have you thought about just replacing the rear 02 sensors, with higher miles, they can become less efficient, won't hurt to try

[neilvan]

cars has 124km on it(75mi?) on it so fairly low mileage. Also the problem only started when the downpipes were swapped over.

I made sure I got the connections right. Is it possible I swapped the sensors to the opposite downpipes and its throwing these codes? Rear O2s usually dont do much other than monitor the delta change from the front O2.