WASHINGTON - The National Highway Traffic Safety Administration said it has upgraded its safety investigation into whether Volkswagen Passats have a defect that poses a fire engine risk. 

The agency said it has received 14 complaints alleging the fire risk in model year 2001-07 Passats and 2006-07 versions of the Passat Wagon. 

NHTSA conducts such probes to determine whether a safety recall is at all warranted.