this is the 3rd time in 6 months my check engine light has come on the on 2011 Chevrolet Impala

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dealer keeps telling me its the gas cap. i know i'm putting the gas cap on correctly. what else can it be and why isn't the dealer looking for something else? this is making me crazy.
(2) Answers
I will assume the engine code says evap. system leak detected small. One possibility is the gas cap but, any hose or vacuum line break or component issue that has a leak can could throw this code. It is an emission recovery leak and the best way to find it is with a "smoke test". Inform the dealer you need this test performed to solve the issue.
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