Ford Motor Co. Continues to Improve its working relationship with its North American suppliers, while Toyota Motor Corp.'s and Honda Motor Co. Ltd.'s dealings have slipped, a recent study reveals.

The latest study by Birmingham, MI-based Planning Perspectives Inc. compiles the Working Relations Index of North America's six largest auto makers — Toyota, Honda, Ford, General Motors Corp., Chrysler LLC and Nissan Motor Co. Ltd.

PPI created the index system eight years ago and determines OEM scores based on confidential interviews with suppliers. This year, the firm conducted an online survey of executives at 231 suppliers between February and April.

The working relationship index consists of 17 variables comprising five components that PPI says are the “principal drivers of supplier working relations.”

Scores range from 0-500, with 500 indicating the strongest relations. Demographically, the study's respondents represent 28 of the top 50 North American suppliers, 43 of the top 100 and 58 of the top 150.

PPI President and CEO John Henke Jr. admits he is surprised by Ford's rapid ascent. “Ford's (rating) has gone up by 43% in the last two years,” he says. “I've never seen it happen before.”

Henke credits Ford's rapid improvement to Paul Stokes, who last year was named the auto maker's executive director-global vehicle production purchasing for the Americas. Stokes came to the U.S. in December after several years with Ford of Europe's purchasing team.

Although Toyota's and Honda's scores dropped this year, the two auto makers still claim the top spots in the survey.

Honda leapfrogs Toyota as the top-ranked auto maker among its suppliers, with a score of 349, down from prior-year's 359 but still besting Toyota's score of 339.