"The Karma performed exactly as it was designed to," Tom LaSorda said in a letter sent to customers. "The onboard diagnostics detected a fault and entered a protection mode that shut the car down to protect other components. We are sorry for the inconvenience this caused the customer."

A Karma that Consumer Reports purchased for $107,850 died on March 7 during speed calibration testing.

Consumer Reports said in a blog post that its Karma had been returned with a new battery pack. The highly influential consumer magazine said the battery light on the car's dashboard lit up during the test drive and the car would not restart after it was parked.

Fisker has benefited from the publicity generated when actor Leonardo DiCaprio was handed the first Karma last summer and pop idol Justin Bieber received one as a gift this month.

But it also had to recall over 200 Karmas last year and briefly halted sales in January over a software issue.

LaSorda said in the letter dated March 13 that he has put in place a "SWAT team" of 50 engineers and other consultants to identify any problems or other issues experienced by Karma owners. He said new software has been developed and installed in a large number of cars that were being tested "round the clock."

"As soon as this procedure is complete we will send updated software out," he said.

LaSorda assured customers he is personally involved in all the company's initiatives and promised them "complete peace of mind." In acknowledging that new technologies sometimes need "updates and refinements," he said Fisker has worked to address customer concerns quickly.

Fisker previously said it had more than 400 Karma sedans already on the road in the United States.

LaSorda, a former executive at General Motors and Chrysler, was named Fisker CEO last month, a little more than two months after joining the company's board.

Consumer Reports said the dealer repair invoice said the problem was "duplicated repeatedly" and a fault was found in the car's battery and inverter cable.

"We now have a brand-new lithium-ion drive battery pack provided under warranty, though likely costing as much as a small, fuel-efficient car," said Consumer Reports, which added it will complete its testing of the luxury car.

A123 Systems Inc, which supplies the batteries for the Karma, referred questions to Fisker.

The breakdown of the Consumer Reports car was more bad news for a company that has found itself under the microscope.

Over the last month, Fisker changed its CEO and halted work at its U.S. plant as it renegotiates the terms of a $529 million loan from the U.S. Department of Energy.

Fisker had already recalled 239 Karmas last December due to a possible battery defect and in January it halted Karma sales for four days to fix a software malfunction that at times triggered warning lights while temporarily freezing navigation systems. ID:nL1E8CKEI8]

Fisker builds the Karma in Finland and plans to build a second model, the Nina sedan, at its Wilmington, Delaware plant, a former GM factory.

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