I just bought a 2010 Ford Fusion SE at a dealer and it has that no-gas-cap fuel inlet. First day I had it, the dash had a text warning "Check fuel fill inlet", then later on the highway, the check engine light came on. Had the codes read, it came back P0455 and P0457. I can sometimes clear the text warning by putting gas in the tank and pulling out the nozzle quickly, but it can recur with the next filling (hit or miss.) Check light stays on all the time. As car is covered by the Lemon Law (just got it a few days ago), they are liable for repairs to make it pass Emissions.
Dealer's mechanic says cause is either purge valve at tank or pressure(?) valve in engine that regulates EVAP canister gas vapor flow, and he says they are each "a couple of hundred dollars" He will put the car up on lift Monday to isolate the leak. Are the valves really the most likely cause (this car has 85,000 miles)?