Clunker hangover hammers September U.S. vehicle sales, and analysts expect among the weakest sales rates this year.

A plunge in consumer demand after the cash-for-clunkers program likely dragged the September sales rate back to the low levels seen in the first half of this year.

Automakers will tally vehicle sales at an annual rate of 9.3 million units in September, according to the average forecast of nine analysts surveyed by Automotive News.

That sales rate would tie March results for the second-lowest rate this year. Analyst said the Detroit 3 and the biggest Japanese companies will post declines tomorrow, with Ford Motor Co.’s sales being closest to year-earlier levels.

Demand was weakest in the first half of the month, analysts said. The federal government clunkers program, which ended Aug. 24, had stifled this month’s sales by draining inventories and pulling ahead buyers who would have made their purchases later in the year.

“What we’re hearing from dealers in the beginning of the month is that there were no customers — but then there weren’t any products to sell, so it really didn’t matter much,” said Jessica Caldwell, a senior analyst for the consumer auto site Edmunds.com. “If you had been shopping for a while and you didn’t have a clunker, you were probably a bit disappointed because there wasn’t much of a selection, and dealers weren’t as flexible with pricing.”

Shrinking inventories

The industry started September with a 30-day supply of vehicles, half the level analysts recommend. By the end of the month, Caldwell said, automakers had produced more vehicles, giving customers better options.

“We’re kind of in a correction stage from where we were at the end of the clunkers program,” she said.

That boost in output helps account for the difference between the seasonally adjusted annual rate of 8.8 million units that Edmunds.com predicted halfway through September and the 9.3 million rate it forecast late last week.

The six analysts who made predictions for the Detroit 3 said Ford’s sales would slide an average of 5 percent from September 2008. Ford, coming off its second-straight monthly gain, stands to benefit from its 36.3 percent sales drop in September 2008, which was the worst of the five top-selling automakers that month.

General Motors Co. will see sales fall 45 percent, the analysts said. GM’s sales last September declined 16 percent, compared with an industrywide slide of 27 percent, partly because of the automaker’s late-August and early September employee-pricing discount in honor of the company’s 100th anniversary.

Chrysler Group’s sales are projected to drop 42 percent

Asian declines

The two analysts who estimated results for overseas-based automakers predicted American Honda’s sales would fall an average of 13 percent, Toyota Motor Sales U.S.A.’s 10 percent and Nissan North America’s 7 percent.

Most analysts released automaker-specific forecasts adjusted for selling days. September 2008 had one fewer selling day than this month does, meaning an unadjusted percentage decline will be about 4 percentage points smaller than adjusted ones. Automotive News does not account for the difference in selling days when it reports monthly sales results.

Reuters said its survey of 41 economists yielded a median sales rate of 9.5 million units. Bloomberg News’ poll of eight analysts showed an average of 9.3 million.

The end of the cash-for-clunkers program also sent the U.S. vehicle mix back to more typical levels, analysts said. Credit Suisse analyst Christopher Ceraso predicted that trucks would outsell cars in September for the first time since January before falling behind again in the coming months.

Languishing demand

Annual sales rates had remained at 27-year lows before July, drifting between 9.1 million and 9.9 million units. In July, the federal government launched cash for clunkers. The program’s offer of up to $4,500 for consumers who traded in gas guzzlers for new vehicles with better fuel efficiency pushed July sales to an annual sales rate of 11.1 million units and August’s to 13.7 million units.

The August rate was the highest since August 2008. Sales for August of this year grew 1 percent from year-earlier levels for the first monthly increase since October 2007.

If September’s results indicate demand strengthened during the month, that bodes well for the rest of the year, said Ford sales analyst George Pipas.

“That might have something to say about how we enter the fourth quarter,” he said. “If it doesn’t improve” from early September levels, Pipas said, “that would raise a red flag.”