According to "The Mentalist" Fan Site, Patrick Jane's car is a Citroen DS. It was produced between 1955 and 1975 and designed by Flaminio Bertoni.
In episode 117, Patrick Jane drove a Citroen DS21, known as Deesse or Goddess. This car was third in the 1999 Car of the Century competition and made advances in road handling, braking and quality of ride. Warner Brothers originally had a vintage 1972 Citroen DS 20 in its inventory, which was used in the movie "Speed Racer" from 2008. For the purposes of "The Mentalist," the car was shipped from Germany and painted from red to eggshell blue. The Citroen DS is credited with saving President De Gaulle from assassination.