Seven years worth of Ford Motor Co.’s most-popular SUV model are a step closer to recall in the U.S. over mounting reports of exhaust fumes leaking inside and sickening drivers.

The National Highway Traffic Safety Administration this week took an interim step toward prompting the recall of 1.3 million 2011-2017 Ford Explorers, including 2016-2017 Explorer Police Interceptor models, linked to accidents and illnesses consistent with carbon monoxide exposure. This comes more than a year after the NHTSA first started looking into odors and exhaust issues in the vehicles.

The NHTSA said on its website that it has upgraded the probe to an “engineering analysis” after receiving at least 2,719 complaints pertaining to those model year Explorers.

In an interview with CBS News last month, Ford spokeswoman Elizabeth Weigandt said a closer analysis of the car revealed a carbon monoxide concentration of 13 parts per million. The current permissible exposure limit established by the Occupational Safety and Health Administration is 50 parts per million.

Three crashes and 41 injuries have been potentially linked to the issue since July 1.