The Tarrant County Medical Examiner's Office said two were pronounced dead at a hospital soon after the crash. The other two died early Sunday.
Southlake police Officer Roderick Page tells The Dallas Morning News investigators are still trying to determine whether driver error or a vehicle malfunction caused the crash.
The car was a 2008 Toyota Avalon, among the models recalled last month over concerns about gas pedals getting stuck on floor mats and causing sudden acceleration.
