Kennybuck

Hey this is my first post been reading for a while and haven't seen this problem yet . Have a 07 crate LS2, Tremec 5 speed, 3.42 rear, Speartech wiring harness for fuel injection, and stainless long tube headers that I had ceramic coated. My problem is this code can and will come up at any time ( 2135 ) it is an o2 code, I have a Matco Tools reader and can erase it but it comes right back sometimes and sometimes not ! What can I do to get it gone, aggravating me to no end? Any help would be greatly appreciated !