alt Hacker NewsWhat about using ForSCAN? It allows anyone with the software and a dongle to monitor and to update modules in the ECU AFAIK. I paid under $100 (can't remember) for a dongle and downloaded the free software and it is extremely handy working on one of my vehicles. The other two Fords I own are both pre-OBDII so there is less bullshit on them to begin with. Ford forums are full of owners who use ForSCAN to modify their vehicle's operation. Lots of hacks available.
Just do as /u/bigfatkitten suggests and get the service manuals when you purchase the vehicle.
ForSCAN is awesome but it's an orthogonal conversation since it's a reverse engineered diagnostic tool rather than a first-party one. If we expand the conversation to that space there are tons of options with varying capabilities depending on manufacturer, including also pirating the OEM tools directly. Also worth noting that ForSCAN also doesn't _quite_ support all common operations, for example Remote Keyless Entry enrollment on newer BCMs with push-to-start needs FDRS still.