Hundreds of people wearing white protective suits sat or stood in front of the grounds where the auto show is being held. The demonstration was organized by an alliance of groups called "Sand im Getriebe" — roughly "spanner in the works."
Other entrances to the show, which opened to the general public on Saturday and runs until Sept. 22, remained open.
The show already attracted a demonstration by thousands on Saturday, many of whom cycled into the city along highways temporarily closed for the occasion. Police put turnout for that protest at 15,000, while organizers said 25,000 participated.
Environmental groups say the trend toward bigger and more powerful cars, particularly SUVs, is eating into the fuel efficiency gains of recent decades.