The three-member committee heard testimony Tuesday from Hendrick Motorsports and NASCAR and ruled unanimously in favor of the sanctions.
Knaus was suspended six races and find $100,000; five-time NASCAR champion Jimmie Johnson was docked 25 points and car chief Ron Malec also was suspended six races.
Team owner Rick Hendrick says they will appeal to the National Stock Car Racing chief appellate officer.
Knaus can work at Bristol this weekend while the case is under review.
The No. 48 Chevrolet had illegally modified sheet metal between the roof and the side windows - the area known as the C-posts.