Sauter was docked 25 points by NASCAR. It knocked him from first place into a second-place tie with Jeb Burton, 13 points behind new leader Matt Crafton.
Crafton and Sauter are teammates at ThorSport Racing.
The illegal fuel cell was found on the No. 98 Toyota during an opening day inspection and was not used in the race. NASCAR also suspended crew chief Joe Shear four races and fined him $10,000.
Sauter won the first two races of the season and finished fifth at Kansas. He's finished fifth or better in all four Truck Series races this season.