This question is more specifically related to California and Nevada testing.

In newer cars, isn't it the case that when they run the smog test they only plug into your OBD2 port to check for smog related fault codes? (They don't actually stick that device up your tailpipe to measure emissions.) And if this is the case, would a catless exhaust with the missing O2 sensors coded out, pass smog since no fault codes would be present?

 

In my experience, CA puts a sniffer in the tail pipe, and checks the OBD2. It has been over 4 years since I lived there though, so it's possible they changed their test.

 

I running catless & smog testing isn't an issue until after 5 yrs as in a 2007 997tt which is when you have to get tested every 2 yrs & yes they use a sniffer ,so you have to switch back to cats or find a SMOG GUY !!

 

+1 they do still sniff. But yes they hook in and connect with the car now. I have some ideas. If you ever need help pm me.