I have a 2010 Tundra 5.7 that is Flex Fuel. I keep getting an engine light, I purchased a new gas cap from the dealer but the one they gave me was for a NON Flex fuel vehicle. They said it didn't make a difference but now when fuel level drops below half a tank I get an engine light again. Does the type of cap Flex vs NON Flex make a difference. It is throwing the same codes as before. Any insight would be appreciated.