Jimmie Johnson says he was "shocked" to learn NASCAR was looking into potential infractions by his No. 48 team for altering the car's side skirts following Saturday night's All-Star race.

NASCAR competition officials reviewed the tape and determined Johnson's crew did not make an unapproved adjustment during a late pit stop at Charlotte Motor Speedway. Johnson's team was issued a warning by the sport's governing body but no punishment was levied.

Johnson says NASCAR "calmed down" after reviewing video.

Side skirts are the sheet metal in front of the rear tires, and unapproved flaring can potentially improve air flow and give a team an unfair advantage.