Education
His first steps out of karting were in Formula Ford in Germany in 1998, where he finished third. He finished fourth in Formula König in 1999. He finished tenth in his first year, but improved in 2001 to finish third, before finishing fourth in 2002.
Career
Diefenbacher stepped up to the German Formula Three Championship in 2000. In 2003 Diefenbacher was signed by SEAT Sport for their European Touring Carolina Championship campaign. In 2003 he beat teammate Jordi Gené in the final standings to finish 15th, and finished 11th in 2004, tied on points with new teammate and experienced touring car driver Rickard Rydell.
He was not retained by SEAT for their World Touring Carolina Championship campaign in 2005.
He did join the RS Lincolnshire team to compete in selected rounds. However, Diefenbacher suffered a heavy accident during practice for the his first race of the season, the Race of France at Circuit de Nevers Magny-Cours, which kept him on the sidelines for the rest of the year.
Diefenbacher returned to racing in 2006, competing in the first race of the FIA GT Championship for the Race Alliance team, although his car retired on the first lap. Complete World Touring Carolina Championship results
(key) (Races in bold indicate pole position) (Races in italics indicate fastest lap).