DETROIT (AP) -- General Motors Corp. will stop making Chevrolet Malibus and Saturn Auras with an early generation gas-electric hybrid engine system, but engineers are working on a more efficient version of the system, a company spokesman said Thursday.
"Mild" hybrid versions of the midsize cars aren't selling well because they cost about $4,000 more than base models but only get four more miles per gallon of gasoline.
And models equipped with a four-cylinder engine and six-speed automatic transmission, which cost about $900 less than the hybrid, get only one mile less per gallon on the highway and four miles less in the city.
"We've seen a lot of people go for the four-cylinder six-speed," GM spokesman Terry Rhadigan said. "That may have had an impact on why they're (hybrids) plentiful in the marketplace."
Rhadigan says the new version will debut with new models in the summer of 2010. He would not identify which vehicles will get the new system.
Currently the GM mild hybrid system, which came to market in 2006, cuts off the engine when the car stops and uses an electric motor to help the gasoline engine get the car going again. Rhadigan would not give details of the new system.
GM sold 706 Malibu hybrids and 35 Aura hybrids in May, compared with a total of 14,098 Malibus and 2,235 Auras for the month, according to Autodata Corp.
Rhadigan said the cancellation of the Malibu and Aura hybrids is not an indication that GM is backing away from the technology. The company, he said, will have 14 gas-electric hybrids on the market by the end of 2012.
"This is not a departure in any way," Rhadigan said. "We're going to have and continue to introduce hybrids into the marketplace across the GM lineup."
Despite the cancellation, GM learned from its mild hybrid experience and applied those lessons to other hybrid systems, Rhadigan said.
GM also has a different hybrid system in its larger sport utility vehicles and pickup trucks, but its sales are slow as well. That system relies on a computer to determine the most efficient combination of two electric motors and one gasoline engine.
The same system is in the Saturn Vue midsize sport utility vehicle, which gets 25 miles per gallon in the city and 32 on the highway with a base price of almost $29,000. But GM is rolling out new gasoline-powered midsize sport utilities this summer with only slightly lower gas mileage with base prices just over $23,000.
Ford Motor Co., GM's crosstown rival, this year came out with the midsize Fusion hybrid sedan, which gets 36 miles per gallon on the highway and 41 in the city.
The company pushed to get the car over 40 miles per gallon to differentiate it from the competition and build a larger gap between it and the gasoline engine versions of the same car, said Nancy Gioia, Ford's director of hybrid vehicle programs.
Initially the Fusion hybrid got to 39 miles per gallon, but engineers were challenged to go back and get it over 40, she said.
"There's a big mental difference between 39.999 and 40," Gioia said. "So we went back to the labs again and said there were some things that the team would continue to refine."