I had a very similar experience. I bought mine at an auction, I am an RV dealer, not a car dealer. Got a good deal. I was getting really strange codes and readings. I replaced what seemed like every sensor. I went so far as to replace the main engine wiring harness. I FINALLY tucked tail...
I had an exhaust shop tell me my codes are caused by clogged cats and blown turbos. I used Cataclean and put on a UPR oil catch can. Problem solved. Turbos are designed to spit oil under pressure. I had to teach that to men at an exhaust shop. SMH. (Blonde Girl)