Hi, I been doing a search on the Sub O2 Sensors from the OBDI SC400. What I read from the search result, I didn't really find a exact answer for what the Sub O2s really do. I just figure learning more about out cars wouldn't hurt.

Thanks

 

Also, are they any threat to CA smog check if they dont work?

 

they check to make sure that your cats are working.
as long as your cats are working properly shouldn't make a difference.