Grohs began racing in 1973 with a Porsche 911, recording four wins that season and attracting an invitation to race for BMW's Team Faltz. In 1974 he contested the German Renault 5 Cup for BMW, winning six races and finishing second in the championship. His first full season in the Deutsche Rennsport Meisterschaft (DRM) followed in 1975 for Team Faltz, where he recorded his first wins but also suffered a serious crash at the Nürburgring. That year he shared a car to win the 9 Hours of Kyalami alongside Jody Scheckter.
The 1976 season brought international BMW racing, partnering Grohs with some of the era's most prominent names: Hans-Joachim Stuck, Ronnie Peterson, Gunnar Nilsson, Jody Scheckter, and John Fitzpatrick. Grohs later recalled: "Only Stuck and Petersson were a little faster, but partnered with Petersson, we could never finish a race." National DRM competition continued in 1977 with a FIA Group 5-specification BMW 320, placing him against the BMW Junior Teams.
The most severe incident of his driving career came in 1978 when he rolled seven times on the Nürburgring Nordschleife. He escaped injured but shaken.
From 1975 onwards Grohs was a regular in international endurance racing. His World Sportscar Championship appearances spanned BMW Alpina machinery in the 1970s and increasingly competitive Porsche campaigns from 1980. Racing with the Vegla Racing Team (operated by Joest Racing) in a Porsche 935, he finished eighth overall at the 1980 24 Hours of Le Mans — first in class — alongside Dieter Schornstein and Götz von Tschirnhaus. The same crew returned in 1981, finishing tenth overall and third in class with the Porsche 935-K2.
In 1981, operating across multiple entries, Grohs achieved his best championship result: second in the World Sportscar Championship drivers' standings with 116.5 points, scoring outright wins at Mosport and Road America while racing for Andial Racing. He also took a class win at the 1981 6 Hours of Silverstone with the Vegla team's Porsche 935J.
His Porsche 956 and 962C campaigns with Brun Motorsport, Obermaier Racing, Dauer Racing, Porsche Kremer Racing, and Joest Racing extended through the late 1980s. His 1983 season with Brun Motorsport produced a fourth-place result at the 6 Hours of Spa and nineteenth overall in the championship. Further top-six results with Obermaier Racing and through the Dauer/Joest connections continued into 1990.
Grohs made seven appearances at the 24 Hours of Le Mans between 1976 and 1988. His best overall result was eighth at the 1980 race driving the Vegla Porsche 935. At the 1976 race he co-drove a BMW 3.5 CSL for BMW Motorsport with Sam Posey and Hughes de Fierlandt, finishing tenth.
Grohs competed in German touring car racing through the Deutsche Tourenwagen Meisterschaft and later the Super Tourenwagen Cup during the late 1980s and 1990s. He retired from the Porsche Carrera Cup and regular circuit racing in 1997, though he continued occasional appearances on the Nürburgring. His 50th start in a 24-hour marathon event came at the 1999 24 Hours of Nürburgring.
In 1997, coinciding with his retirement from active driving, Grohs founded Grohs Motorsport, a team that competed in German circuit racing championships.
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