The car's exhaust was close to an intake for the home's air conditioning, which apparently spread the colorless and practically odorless gas throughout the residence, sheriff's Sgt. Allen Lee said. The car's ignition was on, but its gas tank was empty when rescuers arrived.
There was no sign of forced entry and the bodies had no visible injuries. The victims all appeared to have been sleeping.
"We don't want to speculate but it appears like a family that just went to bed," Lee said.
A neighbor with a key to the single-family home went to check on the residents after not seeing the children during the day, Sheriff Kevin Beary said. After seeing the bodies, he immediately left and called authorities.
The victims were two men, a woman and three boys. No identities were released.
"Unfortunately, there is an air handler from an air conditioning unit in very close proximity" to the vehicle in the garage, Lee said. "What our early tests have shown is that it would have been able to suck that carbon monoxide in the home and distribute it through the air conditioning vents."
Medical examiners waited for the home to be cleared of gas before entering to begin their investigation.
The house is located in a community east of Orlando in a fast-growing part of the county.
Carbon monoxide poisoning claims approximately 165 lives a year, according to the U.S. Fire Administration.