also have you got the camera set to outdoor mode (whatever that is)

Yes you need the sun behind you but even better wait for a nice day that is a bit overcast so there no direct sun light on the car this will stop the oposite afect of the problem you are having where there is to much sun and you get patches of shiny bits on the car where the sun is reflecting off the car and then you dont get any shadows too, just a nice clean picture.

Best time of day for taken photos is 2 hours after sun up and 2 hours before sun down - the orange light is very good then. Set camera to 5.6 and it gives a crystal picture of central image as well as making the back-ground a bit out of focus, so looks ace.