Ford Motor Company (NYSE:F) may be in trouble as the company faces a federal probe over its Explorers that may leak carbon monoxide.

The National Highway Traffic Safety Administration (NHTSA) announced Thursday that it is expanding its investigation to determine whether or not carbon monoxide is leaking from some Ford SUVs. Various reports have accused the company’s vehicles of having a flaw in their design.

At least 791 formal complaints have been filed from owners of Ford Explorers model years 2011 through 2017. A year ago, the NHTSA initiated the probe after receiving 154 complaints from consumers who have been driving the aforementioned vehicle, but only through model year 2015.

There have also been an additional 2,051 complaints that car owners filed with the manufacturer, and at least 41 injuries have resulted from the alleged flaw.

Some police departments use Ford Explorers that are designed to help facilitate law enforcement duties — called the Police Interceptor Vehicle — and at least 60 have been removed from being used by authorities in Austin, Texas.

One officer reported feeling sick while driving the vehicle, causing him to nearly drive off the road. He has filed a lawsuit against Ford as he had to take a medical leave after being poisoned by carbon monoxide.

“A dedicated Ford team is working with police customers, police equipment installers, Police Advisory Board members and NHTSA to investigate reported issues and solve them,” Ford said in a statement. “Customers with concerns about Explorers and Police Interceptor Utilities can call our dedicated hotline at 888-260-5575 or visit their local Ford dealership.”

F stock fell 0.1% Friday.