2006 Scion xA Check Engine Code 0012 timing off

I went to an auto store and they ran a diagnostic with their mini computer. It came up code 0012 Camshaft timing over advanced or blocked oil passage or mechanical timing fault or failed ocv pr vvt controller assembly fault. Does anyone know about how much these types of problems will cost me to have repaired or how accurate these mini computers are. I ask since my check engine light turns off after I put gas in the car and tighten the gas cap.