Registrations in the EU and European Free Trade Association (EFTA) countries dropped to 1.77 million cars last month from 1.84 million a year earlier, the Brussels-based Association of European Carmakers said.
The auto industry is facing a downturn in European demand just as it struggles to make drastic cuts to average fleet carbon dioxide emissions, or face massive fines.
Nissan deliveries were down 29.4 percent in March, broadly in line with their decline for the first quarter as a whole, as the Japanese brand reins in less profitable sales to car rental firms and other heavily discounted channels.
Ford, which is restructuring its European operations to address a weak European performance and the looming regulatory emissions hurdles, saw March registrations drop 15.5 percent.
Sales of Mercedes maker Daimler tumbled 14 percent, while Fiat Chrysler's sales fell 11.7 percent.
Overall, European registrations for the first quarter fell 3.2 percent, the association said.
(Reporting by Laurence Frost; Editing by Leslie Adler)