|Chevrolet is asking owners of about 4,000 Volt plug-in hybrids from the 2013 model year to bring their cars to dealers for a software upgrade. Michelle Malcho, a spokeswoman for General Motors, said in a telephone interview the upgrade was necessary to ensure the Volt would avoid losing power when in motion.
Ms. Malcho said the problem involved a delayed-charging function: a feature that allows owners to preselect a convenient time to charge the Voltís batteries ó when electrical rates are low, for example.
When that option is selected, however, a software malfunction may cause the electric motor to shut off at a different time, even when the vehicle is being driven, she said, forcing the driver to seek a safe place to stop the vehicle. The power steering and brakes still work in this situation, she added.
Typically, the National Highway Traffic Safety Administration requires a recall for problems involving stalling or a sudden loss of power. But instead of a safety recall, the agency is allowing G.M. to conduct what is called a customer satisfaction campaign to address the problem.
A customer satisfaction campaign is less demanding than a recall, which carries legal requirements for the automaker, including the reporting of repair-completion rates.
Kevin Kelly, a spokesman for G.M., said the automaker did not regard the Voltís loss of power as a safety issue because owners could immediately prevent the problem by disabling the delayed-charging feature.
ďIt is a simple toggle-through on the charge mode setting that alleviates the issue,Ē he said. The vehicle can be restarted several minutes after the loss of power, he added.
But Clarence Ditlow, the executive director of the Center for Auto Safety, wrote in an e-mail that the loss of power ó or stalling ó could result in a crash and was clearly a safety issue that should require a recall.
Ms. Malcho said the problem, which G.M. learned of from several owner complaints, affected only 2013 models. The automaker was not aware of any accidents related to the problem.
She added that N.H.T.S.A. approved the customer service campaign. In an e-mail, Karen Aldana, a N.H.T.S.A. spokeswoman, declined to corroborate Ms. Malchoís claim or comment as to why a loss of power would not be considered a safety issue.
ďThe agency will continue to monitor the issue and will take appropriate action as warranted,Ē she wrote.