Automotive News reports that if a driver leaves their Volt running in the electric mode, the vehicle will drain the battery and cause the gas engine to kick on.
"If the gas engine runs for a long period of time within an enclosed space, such as a garage, carbon monoxide could build up," GM said in a statement.
GM says they are aware of two people who had carbon monoxide exposure from the Volt.
At the moment, the Volt has a chime that come on if a driver exits the vehicle and leaves it running.
GM will issue a software update that will limit the Volt's idling time when left in the 'On' position.
Source: Automotive News (Subscription Required)