The auto racing channel SPEED said late Sunday the cars of both Nextel Cup drivers were seized after unapproved aerodynamic modifications to their cars.
"We found unapproved devices that, in the opinion of our competition folks, enhanced the aerodynamic performance of those cars today," NASCAR Vice President of Corporate Communications Jim Hunter told SPEED.
Hunter said Kenseth's car had holes drilled in the rear wheel wells, but he did not know specifics on Kahne's car.
Both drivers are still in the Daytona 500, but will have to start Thursday's Gatorade Duel at Daytona qualifying races from the back of the field.
The Toyota of Michael Waltrip also had a problem, but it was found before qualifying and NASCAR officials allowed him to run.