In 2003, Carpenter began competing in the IndyCar Series for PDM Racing in the No. 18 Dallara-Chevrolet. Carpenter made his debut at the Delphi Indy 300 at Chicagoland Speedway; he started in 16th place and finished in 13th place. Carpenter then competed at the Toyota Indy 400 at California Speedway, starting in 17th place and finishing in 13th place, two laps down. At the season-ending Chevy 500 at Texas Motor Speedway, Carpenter started in 22nd place and finished in 21st place due to alternator problems after completing 69 laps. Carpenter finished the season ranked in 26th place, with 43 points. In 2004, Carpenter ran his first full-time season for Red Bull Cheever Racing in the No. 52 Dallara-Chevrolet. At the season-opening Toyota Indy 300 at Homestead-Miami Speedway, Carpenter started in 9th place and finished in 12th place. During the season, Carpenter struggled to match the results of teammate Alex Barron. Carpenter's best finish was 8th place at the Belterra Casino Indy 300 at Kentucky Speedway. Carpenter qualified for the Indianapolis 500, starting in 16th place and finishing in 31st place due to a crash after 62 laps. Carpenter finished the season in 16th place, with 245 points. For 2005, Carpenter's stepfather Tony George started a new team called Vision Racing after purchasing the equipment from Kelley Racing. Carpenter drove for the team in the No. 20 Dallara-Toyota. During the year, Carpenter and the team struggled; his best start was 16th place at the SunTrust Indy Challenge at Richmond International Raceway. Carpenter's best finish was at the Firestone Indy 200 at Nashville Superspeedway with a 10th-place finish, one lap down. Carpenter qualified for the Indianapolis 500, starting in 26th place and finishing in 11th place, one lap down. Carpenter finished the season in 18th place, with 244 points.