"With mixed economic signals, it certainly looks like U.S. auto sales may have peaked in 2015," said Jeff Schuster, head of forecasting at LMC. "However, it is important to focus on the sustainable high level of demand. Peak does not mean doom and gloom, and while the industry faces risk, it is not destined for a pullback.”

The consultancies said they expect August U.S. total auto sales of 1,492,700 vehicles, from 1,574,938 a year earlier. Automakers will report sales next Thursday.

Shares in the biggest U.S. auto companies General Motors Co (>> General Motors Company), Ford Motor Co (>> Ford Motor Company) and Fiat Chrysler Automobiles (>> Fiat Chrysler Automobiles NV) have been pressured because big investors expect sales to slide from their peak.

(Reporting by Bernie Woodall; Editing by Nick Zieminski)