AUSTIN (KXAN) — After months off the street, all but one vehicle in a fleet of Austin Police Department Ford Explorers is back in service. The 400 vehicles had been pulled following carbon monoxide leak incidents.

In July 2017, a number of officers became sick after carbon monoxide leaked into their vehicles, but APD reported the department experienced its first exposure to CO in March. One of the officers affected sued both APD and Ford.

• Video shows moments APD officer realizes something is wrong with his patrol car

An investigation revealed the tailpipes weren’t clearing the back of the vehicles, causing the gas to seep inside. The vehicles were fixed, and new carbon monoxide detectors were installed.

APD is working to diversify its fleet, as Ford Explorers make up about 60 percent of it.