On January 21, 2011, the Office of Defects Investigation (ODI) opened a Preliminary Evaluation (PE11-003) to investigate alleged wheel stud fractures in certain model year (MY) 2010 Ford Fusion vehicles.ODI sent the manufacturer an information request letter dated February 8, 2011 and Ford responded by letter dated March 25, 2011.Ford provided a supplemental response by letter dated July 15, 2011.To date, ODI is aware of 29 complaints related to the alleged defect in the subject vehicles, which now include certain MY2010 Mercury Milan vehicles that are the same or substantially similar to the subject Ford Fusion vehicles in regards to the alleged defect.In total, ODI is aware of 4 reported wheel separation incidents related to the alleged defect in the subject vehicles.The manufacturer's investigation into the root cause of the alleged defect is ongoing.Accordingly, this investigation has been upgraded to an Engineering Analysis (EA11-009) to further study the alleged defect.