The seven times world champion, who sat out morning practice, ended the day as the fastest race driver on the Hockenheim circuit.
BMW Sauber's Polish test driver Robert Kubica topped the timesheets with a one minute 16.225 second lap in the afternoon but Schumacher was second quickest in that session with a time 0.277 seconds slower.
The German is chasing a hat-trick of victories, after winning in the United States and France, to reduce Formula One world champion Fernando Alonso's 17-point overall lead with six races remaining after Hockenheim.
Renault's Alonso had a low-key day, setting the seventh fastest time in the morning and 15th in the afternoon, with temperatures cooled by a rain shower before the start of the second session.
Williams's Austrian reserve driver Alexander Wurz was quickest in the morning in 1:16.349 seconds. Neither he, Kubica nor any of the unsung 'Friday testers' will race on Sunday.
Williams's German rookie Nico Rosberg skidded off in the morning while Midland's Dutch driver Christian Albers pulled over with smoke pouring from the Toyota engine.
The day started with a flurry of technical advisories, with champions Renault challenging and overturning a ban by the governing body on a 'mass damper' device installed in the nose of their car.
The International Automobile Federation (FIA) had outlawed such dampers, used by at least seven of the 11 teams, after the last race amid suspicions they were helping to improve the aerodynamic performance of the cars.
However Renault submitted their spare car for scrutiny with the component still installed.
The race stewards subsequently ruled that it was permissible, a move that could boost Alonso's chances of ending Schumacher's winning run.
Super Aguri ran their new car for the first time at a grand prix weekend with Japan's Sakon Yamamoto replacing France's Franck Montagny in Sunday's race line-up.
