US car sales held up in September despite the weak economy, while the US Big Three producers continued to add market share at the expense of their Japanese rivals, new sales data showed Monday.

A burst of sales of heavier, relatively fuel-inefficient sports utility vehicles and pickup trucks, boosted by increased buyer incentives, helped General Motors, Ford and Chrysler raise their collective market share to 48.1 percent in September, up from 45.2 percent a year earlier, according to company sales reports and analyst Autodata Corp.

Total sales by the three in the month were 506,566 vehicles, 16.9 percent higher than a year earlier, when the industry was still climbing out of the 2008-2009 recession.

The month's total was only slightly down from August, despite worries that falling consumer buying power and political turmoil would hurt sales.

"For GM, all of the factors that say this is a good time to buy a new vehicle outweigh the bad news that appears to be slowing down the broader economic recovery," said Don Johnson, GM's vice president for US sales.

Meanwhile Japanese rivals Toyota and Honda continued to struggle to rebuild from the hit their supply chains took from March's devastating earthquake-tsunami disaster.

Toyota's sales, at 121,541, were still 17.5 percent lower than a year earlier, while Honda, at 89,532 units, was 8.0 percent down.

Nissan, though, stood out with a 25.3 percent year-on-year sales rise to top Honda with sales of 92,964 units.

Edmunds.com analyst Michelle Krebs said higher incentive offers by Chrysler and GM boosted their turnover.

"GM's gain on sales of its fullsize pickups and SUVs appears to be very much incentives-driven and helped by moderating gasoline prices, as is the case for all trucks and SUVs," she said.

She said Nissan's success arose from its having substantial inventory in a range of market segments.

"Nissan has been very aggressive in using advertising to get out the message that it has plenty of inventory," she said.

Total sales for the first nine months of the year, at 8.6 million vehicles, was 10.4 percent over the same period in 2010, according to Autodata.

In an overall market that shed 2.4 percent in the day, GM's shares dropped 2.2 percent Monday; Ford fell 3.1 percent, Toyota's US traded shares fell 1.9 percent, and Honda's lost 1.4 percent.