New-car registrations in Spain declined 10 percent to 66,925 in August despite a government scrapping plan that was approved in mid-June, data from industry association ANFAC showed.
Registrations rose 1.1 percent in July, the only increase for the country so far this year.
Demand was hit by continuing uncertainty over the health and economic implications of the coronavirus pandemic, ANFAC said.
The Spanish government unveiled a 3.75 billion euro ($4.2 billion) stimulus program starting June 15. The program includes 250 million euros to encourage consumers to replace cars older than 10 years with newer models and more energy-efficient vehicles.
The bonuses range from 800 euros for gasoline and diesel vehicles to 4,000 euros for zero-emissions vehicles.
The stimulus program still has enough funding available to support demand until the end of 2020, ANFAC said.
Sales last month to private customers were down 10 percent to 37,664, according to ANFAC. Sales to companies dropped by 16 percent to 24,230. Registrations by rental car companies rose 22 percent to 5,031.