Sales for September were up 4.5% although YTD they were down 35%. This unusual situation is caused by the COE system, or certificates of entitlement. The government only issues so many and they are bid for by those desirous of buying a new car. The amount available depends mainly on how many cars were scrapped or taken off the road. It's all about controlling the number of cars on the road.
Below the % column is market share and the +/- is shift in that share, comparing the first nine months of 2018 with the full 2017 year. Below green shows market share gain and yellow a drop.
Honda has established itself as 'the' brand with 1 in 5 cars sold bearing their logo. Toyota used to be always the best selling brand but for now it is playing second fiddle. As to why these two brand have nearly 40% of the total I'm unsure. It's not like these are local brands that can count on support in that way.
Data source: LTA Singapore.
Picture source: Car Buyer.