An off-duty Chicago Fire Department lieutenant fatally shot a teenage boy who tried to steal his car Monday morning in the West Side Austin neighborhood, authorities said.

About 9:30 a.m., the 45-year-old lieutenant left his vehicle running in the 1400 block of North Lockwood, when the boy got inside and tried to drive off, according to Chicago Police and Fire Department officials.

The lieutenant fired his weapon at the teen, who was trying to run him over with the vehicle, authorities said.

The boy, identified as 17-year-old Charles K. Macklin who lived in the same neighborhood, was shot in the chest and taken to West Suburban Medical Center in Oak Park, where he was pronounced dead at 9:33 a.m., police and the Cook County medical examiner’s office said.

An autopsy Tuesday showed he died of the chest wound, and his death was ruled a homicide, according to the medical examiner’s office.

The lieutenant has a concealed-carry permit and FOID card, authorities said.

Fire Media Affairs Director Larry Langford confirmed the man’s position with the department. He said the lieutenant was not injured in the shooting, but was taken to a hospital for observation.

Area North detectives are investigating.