SONOMA, Calif. — Jimmie Johnson and teammate Jeff Gordon had an unexpected and unwanted day off Friday.

The cars of defending NASCAR Nextel Cup champion Johnson and series points leader Gordon failed inspection and were barred from all activity for the day at Infineon Raceway, including qualifying.

NASCAR said the No. 24 and No. 48 Chevrolets, both owned by Hendrick Motorsports, had modifications to the front fenders that were deemed illegal during morning inspection.

The Hendrick crews were allowed to repair them and they can race in Sunday's Toyota/Save Mart 350, although starting from the rear of the 43-car field. Gordon, the four-time series champion, is the defending race winner.

"The cars have been repaired and I'm under the impression they will not receive an inspection sticker until tomorrow morning, which will allow the cars onto the racetrack," said Chad Knaus, Johnson's crew chief. "The guys on both teams have done a good job getting the cars repaired. They are race-ready now."

But the damage was already done.

Doug Duchardt, vice president of development for Hendrick, called the modifications an honest mistake.

"We've been evolving and this was just the latest evolution of what we've been doing," he said. "Our understanding is that our cars fit the templates but that they were outside of what they would like to see within the templates."

Gordon came to Sonoma after his wife gave birth to the couple's first child, a daughter, on Wednesday.

"Well, obviously, nothing's going to ruin my day or weekend," Gordon said. "I'm on cloud nine. This has obviously been pretty devastating news at the racetrack. ... This definitely puts us in a box and we're going to have to work our way out of it."

The five-time Sonoma winner said pit strategy is going to be "extremely important."

"We're one of the best teams out there," he said. "I love the road courses and I know these guys have brought a great race car and I'm looking forward to getting out there, hopefully sometime tomorrow, and seeing what we've got for them on Sunday.

This is the first road race for NASCAR's new Car of Tomorrow, a bigger, bulkier and reputedly safer car that's been in development for seven years. It has run in six races this season, all on ovals.