Your problem is not so much the Cat Communications Adapter but with getting hold of a genuine version of the ET software that is required to communicate with the various Electronic Controls Modules (ECMs) on any Cat machine or engine. ET is only sold by Cat dealers - after installing it on your PC and before it can be used "in anger" it needs to be licensed. This can only be done by the dealer who sold the particular copy of the software in the first place. As far as I'm aware, installing the software in your PC generates a random 20-digit License Code, a bit like a piece of Microsoft software. With that code and the details of the Serial Number of the PC on which the software is installed (a single copy of ET is only licensed for use on a single PC) the Cat system generates a 24-digit License Key. When that key is entered into a space in the licensing screen and you click the "Authorize" key, your ET software is fully functional.
I've seen a lot of places offer to sell ET software along with the License Key needed to use it, but I have no idea how good a solution this would be because AFAIK (as explained above) the licensing process does not work that way.
Just as an aside the photo in your link does not accurately represent the latest version of the Comms Adapter. The one showed in the photo is a 171-4400 Comms Adapter 2, the latest version is the 317-7484 Comms Adapter 3. Something also appears to be weird about the price because the latest version of the Comms Adapter sells for around $1000 give or take from a Cat dealer, the Comms Adapter 2 was almost the same price. So the question is how these guys can sell what is allegedly the genuine article for half the price. That does not make sense to me.
