A closing plug for an opening in a body structure of an automobile, wherein the closing plug closes the opening against a passage of fluid and/or gas up to a limit pressure which acts on the closing plug, and allows a passage of fluid and/or gas above the limit pressure, characterized in that the closing plug comprises a base body consisting of a first plastic material, which has a holding section with holding means for holding the closing plug in the opening and a plate-shaped head section provided on one end of the holding section with at least one opening and that the closing plug comprises a sealing body of a second plastic material molded onto the base body in a plastic injection molding process.