But strong gains by import brands in the month kept year-to-date sales only 0.7 percent below last year's record pace.
Among the Big 3, Ford of Canada sales were off 12.8 percent for the month and 13 percent for the eight months. Cars were off 9.8 percent for the month and trucks fell 14.2 percent.
Chrysler sales slid 12.4 percent, with cars down 27.6 percent and trucks off 5.6 percent. Chrysler's sales for the first eight months are down 10.5 percent.
General Motors was off 4 percent from a year earlier, with cars off 6.1 percent and trucks down 1.7 percent. Sales so far this year are down 4.1 percent.
Among imports, European brands edged up 1.6 percent from a year earlier.
The Japanese gained 6.9 percent, while Korean brands surged 45.2 percent.
Honda led all import brands in August with sales of 14,423 vehicles, up 13.8 percent from a year earlier.