You now have an affordable place to shop for all your car hardware and software needs, please don't put off by my cheap prices; if they were no good then I wouldn't sell them, full stop!
Are you a car tuner and need a way of correcting the checksums in your modified binary? Why don't you checkout the ECUFix software here? It is written by us and supported by us.
By far the most popular products I sell are Professional OBD-II interfaces, both the USB and RS232 vareties are hot favourites. These are recommended for use with the excellent AlfaDiag software available on the web.
I am now stocking moulded OBD-II plugs with an open-ended lead for both 12V and 24V types. Don't forget that we also have 12V OBD-II sockets complete with a short length of lead too. You may have heard of the recent series of car thefts by thieves smashing the car window to gain access to the OBD-II socket. Once accessed, it is a relatively simple matter to program a new key transponder to the ECU and simply drive the car away... bye bye....
All this interface work really needs some way of tapping into the data exchange between a commercial device and the car. Here you could do no worse than trying out the OBD-II breakout box, this even comes with a Y lead too.