The National Highway Traffic Safety Administration (NHTSA) has opened an investigation into some 2009 Mazda CX-9 sport utility vehicles (SUV) after reports of a high number of warranty claims for servicing brakes. Reports found that the high number of warranty claims on brakes was due to an internal brake fluid leak from the master cylinder into the vacuum booster. Drivers reported reduced brake effectiveness and extended stopping distances. A preliminary evaluation has been opened to assess the scope, frequency and safety consequences of the alleged defect. If the investigation should lead to a recall, about 40,000 vehicles could be affected.