Gizela Andrade, who has been missing since Sept. 25, was found in the driver's seat of the car, parked in a restricted area.
The white 2010 Toyota Venza was spotted Tuesday night by a Mount Vernon detective, who was searching the area of the Bronx near the Mount Vernon border on an unrelated matter.
He was looking for a place to park when he recognized the car that Andrade was last seen driving, the commissioner said. Paramedics responded and pronounced the woman dead.
Mount Vernon police Commissioner Carl Bell said the preliminary cause of death was an insulin overdose.
Ellen Borakove, spokeswoman for the city medical examiner, said the official cause and time of death were pending further study.
There seemed to be no signs of foul play, Bell said. As a result, Andrade's boyfriend was not considered a suspect, "but if the situation changes, obviously that may change," he said.
It is possible Andrade's car was parked there for a week, but went unnoticed by the police officers who use the area daily.
"We don't know when she got to that spot," Bell said. The NYPD said the car had apparently been there several days.
Bell said there had been no sign of Andrade since she disappeared.
"From the time she left there was no further communications," he said.