2019 is off to a slow start for vehicle sales; averaging 16.6 million through February (average of seasonally adjusted rate).
Click on graph for larger image.
This graph shows annual light vehicle sales since 1976. Source: BEA.
Sales for 2018 were the fourth best ever, but 2019 is off to a slow start.
The second graph shows light vehicle sales since the BEA started keeping data in 1967.
A small decline in sales this year isn't a concern - I think sales will move mostly sideways at near record levels.
This means the economic boost from increasing auto sales is over (from the bottom in 2009, auto sales boosted growth every year through 2016).