The U.S. National Highway Traffic Safety Administration is investigating Nissan Motor Co.'s top-selling model after hundreds of drivers complained a safety system is prone to suddenly triggering the brakes for no apparent reason.

More than 840 Nissan Rogue drivers have complained to NHTSA and the company that the vehicle's automatic emergency braking system activates when there's no obstruction ahead, according to a notice about the probe on the regulator's website. The agency said there are reports of 14 crashes and five injuries linked to the issue.

In a statement, Nissan said it has consulted with NHTSA while investigating the issue internally, and notified customers of an available software update that improves the performance of the Rogue's automatic emergency braking system free of charge.

NHTSA will examine the cause of the unintended braking and whether steps by Nissan to address the issue through customer-service initiatives were suitable. The defect investigation covers more than 550,000 Nissan Rogue sport utility vehicles and is the latest indication transportation safety officials are closely watching for new risks posed by automated driver-assist systems as they become more common on U.S. roadways.

"Nissan is committed to the safety and security of our customers and their passengers," the company said in an emailed statement from its headquarters in Yokohama. "Nissan has investigated this issue extensively and, in consultation with NHTSA, launched field actions notifying affected customers."

NHTSA began evaluating reports of the issue after the Center for Auto Safety made a formal request for a defect probe in March.