The firmware can also change. There are officially 2 different versions of firmware, the 1.2 and the 1.3. Only the very experienced users will be able to tell the difference between a firmware 1.2 and a 1.3 as the basics remain the same. On the internet we can also find the 1.5 version. We bought one ourselves so we can definitely say that it does not exist. It is actually a copy of the 1.2 version called 1.5. You can find in our link tips, how to make sure that the version that you have is the right one.
News :Elm Electronics have just released the 1.4 version of its ELM 327 circuit. View their website for more details. here