YOKOHAMA (Reuters) - Nissan Motor Co Ltd launched a suite of semi-autonomous driving functions on Wednesday stressing they were intended to assist and not replace drivers, just two weeks after similar technology in another maker's car was involved in a fatal crash.

Japan's second-ranked carmaker by vehicle sales said its ProPilot can drive a vehicle on single-lane motorways and navigate congestion. It said the feature will first appear on a Serena minivan model on sale in Japan from next month.

As global automakers race to develop self-driving cars, the safety of current automated systems was called into question by U.S. investigators saying a driver died in a crash while the autopilot of his Tesla Motors Inc Model S was engaged.

While Nissan declined to comment directly on that incident, Executive Vice President Hideyuki Sakamoto said it was important drivers did not overestimate the purpose and capabilities of automated driving functions.

"These functions are meant to support drivers, and are not meant as self-driving capabilities" which let drivers take their eyes off the road, he said. "These are two very different things."

Pushing a button on the steering wheel activates ProPilot, which keeps the vehicle a fixed distance from the car in front without requiring the driver to control the steering, accelerator or brake.

Like Tesla's similar technology, ProPilot requires drivers to keep their hands on the wheel. A warning sign flashes if the wheel is released for more than around four seconds, and an alarm sounds after 10 seconds.

General Manager Tetsuya Iijima at Nissan's Advanced Technology Development department said it was up to automakers to educate drivers about the capability of automated driving functions to prevent misuse that could lead to accidents.

"Naturally, there are limitations to the system, and our job is to communicate what those limitations are," he told reporters.

With ProPilot, Nissan joins many automakers including Tesla, BMW and Daimler AG's Mercedes-Benz in marketing adaptive cruise control and traffic jam assistance.

Nissan will sell its ProPilot-equipped Serena for under 3 million yen ($28,758), making it one of few mid-priced vehicles with autopilot features more common among luxury cars.

The automaker also plans to add ProPilot to Qashqai sport utility vehicle crossover models in coming months, and introduce the feature in the United States and China.

Nissan continues to aim for autonomous multiple-lane driving, including lane changes, by 2018, and functions for full urban driving, including intersection turns, by 2020.

(Reporting by Naomi Tajitsu; Editing by Christopher Cushing)