Reset the ecu. Pull the backup fuse in the engine bay fuse box for 60 seconds...pop it back in, start car. If it comes on again, get an OEM gas cap. I bet the walmart ones are complete pieces.
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2015 Ford Mustang GT Fastback - Ingot Silver - 6M - Performance Package - Gibson Catback, JLT CAI, FR 47lb injectors, BAMA E85 tune, Eibach Sportline, BMR wheel hop kit, UPR oil separator, Steeda shifter bushing/bracket
Team B.O.B.® - Ballaz on a Budget