* Fiat remains top auto seller in Brazil, VW follows
SAO PAULO, Oct 4 (Reuters) - Brazil's car output and sales dropped in September from August, adding to signs of economic weakness in the third quarter after a surprisingly good start to the year.
Automobile production in Brazil dropped 2.5 percent and sales fell 5.9 percent in September from August, the national automakers' association Anfavea said on Friday.
Part of the drop was due to the lower number of business days in September compared to August, according to data from the national car dealers association earlier this month.
Auto output had risen 9.0 percent and sales had slipped 3.8 percent in the prior month, according to previously reported data.
Brazil's economy accelerated in the first half of this year, thanks in part to tax breaks and state-subsidized loans offered by President Dilma Rousseff. Recent data suggests a sharp slowdown in the third quarter, though.
Brazil is the world's fourth-biggest auto market, with Italy's Fiat SpA, Germany's Volkswagen AG and U.S.-based General Motors Co and Ford Motor Co selling more than 70 percent of new cars in the market.
Fiat remained Brazil's top seller of cars and light trucks in September, with about 63,000 new registrations. VW stayed in front of GM, selling some 57,000 passenger vehicles compared with the American automaker's roughly 51,000 cars and light trucks. Ford sold about 28,000 vehicles.
French car maker Renault SA kept its lead over Hyundai Motor Co with about 21,000 new registrations compared with its South Korean rival's roughly 17,000 sales.