In 1998, Johnson started racing in the American Speed Association (ASA) series. He had only raced in six stock car races in his life before the season. Johnson ended the season fourth in points, and he won the Rookie of the Year award. Johnson also started to race in the NASCAR Nationwide Series. He drove in three races during 1998. In 1999, Johnson raced in both the ASA Series and the Nationwide Series. He won twice and finished 3rd in the ASA series. In 2000, Johnson raced the full season in the Nationwide Series. He drove for Herzog Motorsports, and finished 10th in the points standings. He won his first and only Nationwide Series race in 2001 at the Hills Brothers Coffee 300 at Chicagoland Speedway in his 81st start in the series. It was at this time that Johnson was teamed up with crew chief Chad Knaus who he still works with today.