Be a little bit careful if you are going to inject messages onto your cars data busses! For example, the air bag system includes End Of Life functionality to fire the airbags (so they can be safely disposed of), and this is triggered by CAN messages! Yes, it would be very unlikely for you to accidentally send the precise message(s) required but it's not theoretically impossible! And besides such obviously dangerous events, there are a host of less dangerous but potentially costly ones like putting modules into bootloader mode and erasing their memory, that will cost you either a trip to the dealers for a re-flash, or haing to buy some specific recoding s/w for your car!
My suggestion, put your CAN sniffer in to "listen only" mode to start with. This mode means your device is entirely passive (does not even send ack bits) and simply listens to the messages on the bus sent by other modules. Log those messages and you can pretty quickly figure out a lot of obvious stuff (like engine speed, or vehicle speed, or the "turn the heater rear window on" command. More difficult to decipher will be complex rapidl changing data messages for things like engine torque or ABS interventions etc, but it is a fundamentally open protocol so nothing is specifically encrpyted.
Note that on some cars, the OBD port, which is mandated by the regulations to allow diagnostic access is NOT actually on the main powertrain bus, but is behind a gateway module that controls access to the rest of the system. To get all the powertrain data you may need to find and connect into the actual powertrain bus. Fortunately, this is very easy to find, just look for the twisted pairs that make up the bus! (often yellow (CANH) and green (CANL) and you'll definitely find these running from the engine controller to the ABS, the driver display and to the transmission Ecu (if auto)