“We know car sales have been down, but the truck part of the market has been stronger, so this is worth watching, to see if it’s a new trend,” said Jessica Caldwell, an analyst at Edmunds.com, a car-information website. “If trucks fall again in August, this could be something to worry about.”
An acceleration in the auto-sales slowdown could have important political and economic effects. The auto industry is the country’s largest manufacturing sector, and automakers, parts suppliers and dealers together employ more than seven million people. President Trump had hoped the car industry would serve as a job creator as his administration took office. That now seems unlikely because manufacturers are trimming production as sales slump.
In the latest monthly figures, General Motors suffered the most surprising fall, a decline of 15.5 percent, according to the research firm Autodata. G.M. blamed cutbacks in sales to rental car companies, and tough comparisons with July 2016, when it offered big discounts and promotions to drive up sales. Fiat Chrysler reported a 10.5 percent fall in sales, and Ford Motor a 7.4 percent decline.
Each of those manufacturers was hurt by unexpectedly sharp declines in sales of certain trucks and S.U.V.s. G.M. sold 43 percent fewer Chevrolet Traverse S.U.V.s than a year ago, and 15 percent fewer Silverado pickups. Fiat Chrysler’s Jeep division saw its sales tumble 23 percent.
Brett Saslow, owner of Smith Haven Chrysler Jeep Dodge Ram in St. James, N.Y., said Jeep had been hampered as Fiat Chrysler rolled out redesigns of the Cherokee and Compass models. A Jeep pickup that has been in development for the last few years would help sales, he said.
“Very eager for that,” he said. “That would fill a slot for us and there’s demand for smaller pickups with gas prices low.”
A recall forced Ford Motor to temporarily halt sales of its Transit delivery van.
At Honda, overall sales declined 1.2 percent after a big drop in demand for the CR-V, which has been its top-selling model.
Alec Gutierrez, an analyst at Kelley Blue Book, said he was not yet alarmed about weakening demand for trucks. “The segment is at its peak, so we will see some up months and some down months,” he said.
Toyota Motor was one of the few automakers that saw an increase. Its sales rose 3.2 percent, thanks to robust demand for two of its S.U.V.s, the Highlander and RAV4.
One issue that may be at play is a continuing rise in vehicle prices, making new trucks and S.U.V.s an increasing stretch for many Americans. Large S.U.V.s and pickups typically sell for at least $40,000.
In July, the average amount a consumer borrowed to buy a new vehicle was $30,689, 17 percent more than five years ago, according to Edmunds, the automotive data provider. The average monthly car payment was $509.
“That’s a pretty hefty chunk of change for most people to handle,” Ms. Caldwell said.