TOKYO—A semiautonomous Honda SUV was traveling down a test track at 20 miles an hour in March last year when a child-size test dummy moved into the middle of the road. Oblivious, the Honda mowed it down.

It was part of a brutal day of Japanese government testing for Honda Motor Co. , whose vehicle was equipped with a camera and sensors that were supposed to detect obstacles and apply brakes to avoid a collision. The SUV scored 0.2 out of a possible 25 points in the pedestrian portion of the test, the worst among tested vehicles.

With its long heritage of technical prowess, Honda was determined to do better—and it did. But Honda engineering didn’t get it there. The car maker turned to an off-the-shelf sensing kit from Robert Bosch GmbH, the companies said. With the Bosch technology, the new Honda Civic took the same test in November and scored 24.4 out of 25.

Honda’s decision to go shopping points to a radical culture change at one of Japan’s proudest companies, where founder Soichiro Honda in the 1960s said, “We refuse to depend on anyone else.” The struggle at the entrepreneurial success story cuts deep into Japan’s sense of itself as a global leader in technology.

Honda once used staff technicians to design new technologies ranging from engines to the shape of the suspension arms. Today, Honda believes rapid shifts in technology mean it can no longer afford to keep pace working solely on its own.