There is no need for additional +12V supply from car cigaret socket. The schematic gets +12V from OBD socket.
This schematic was used instead of MC33290 in standard OBDuino ISO diagram.
Link:
OBDuinoDiagram - opengauge - Whole diagram of the Arduino board, LCD, interface - Open Source Fuel Efficiency Instrumentation - Google Project Hosting
P.S. Only difference is in 510R, which was increased to 560R (That I found in internet).
P.P.S. 1N4004, 100R was used for protection SI9243 (from SI9253 datasheet).
Best regards