I don't know which browser you use (Internet Explorer?), but I faced problems on this site when using Firefox and derivatives or Chromium. It's not just a matter of invalid security certificates, as usual, but the browser also don't know how to handle the cyphering key of the plate part!
On my computer, it works only with Opera and some lightweight browsers (Midori and Arora), but it asks a lot of clicks to accept several "invalid security certificates". Really weird for a .gov.br site...

This said, and even if this website is primarily aimed at finding stolen vehicles, it does the job for the IMCDb as it gives the make, model and model year of the vehicle (among other details).