No dumb questions there!So the only way to get data from the ODBII port is to query for it, right? Is that how all the CAN bus networks work, or can you just connect and sit and listen?
So for example, if I want to watch what happens when I turn on the turn signal, can I listen for messages on one of the other networks?
Sorry for the dumb questions. I have a lot of software dev experience (especially SOA) but this is my first time toying with cars.
You may want to check out my post Hacking the Jeep Interior CAN-Bus | Chad Gibbons' Blog and the other thread here http://www.wranglerforum.com/f202/hacking-the-can-interior-bus-466730.html for more details on the CAN bus stuff.
CAN itself is a broadcast protocol. Any node on the bus receives all messages from all other nodes. If you hook up a device capable of connecting to a CAN bus, and monitoring it, to the CAN-C (power-train) or CAN-IHS (interior - the dash, radio, etc.) busses you will see a non-stop torrent of data.
What I've done is the basics of performing an action in the vehicle and looking at how the data changes. There are a bunch of tools to help isolate background noise from data that's actually new. For example, the Jeep constantly sends out a 'power on' CAN bus message, among many, many others. If you wanted to see what message gets sent when you press the window down button, it can be a little hard to see amongst all those constant other messages... but the tools (https://gitorious.org/linux-can in my case) can really help with that.
There are some other tools that folks have written to do statistical analysis of how many messages with certain id's are being sent around if you capture everything. That can help you figure out how many unique messages exists.
The diagnostic CAN bus, on the OBD-II port, is a bit different in the JK. It's only there to exchange messages between the scan tool (or whatever) and the TIPM. So by default, it is quiet... you ask it for something, and it tells you. But what we're speculating above is that if you ask it the right things, then it will forward all the traffic off the other busses. Which is convenient from a tooling perspective - physically connecting to the other busses is a bit of a pain.