could a failed (leaking) oil pressure sensor cause a PO455 code?(eval emission system large leak detected)
Nope, P0455 is a gross evap leak, have you checked to see if your gas cap is on tight?
that was the first thing i replaced when the code showed up.
Year and make of car?
2005 chev trail blazer,
As was already said, these two issues are totally independent of each other.
Bought a new gas cap from the dealer, fixed my check engine light for that code I think. 2003 Trailblazer. Agree with others, not related.
Have the system smoke tested. That will pinpoint the leak. Possible that mice have chewed through one of the evaporative emissions hoses, or that a plastic fitting on a hose has cracked.