Can I connect to my car's can bus with an elm327 interface?
I've been fiddeling around with a bluetooth elm327 device I bought a few months ago and am able to get standard obd infos like vin, rpm, speed etc. But as I just read about recently obd2 and can are not the same. I've tried to sniff on my can bus with th AT MA command, but I get no response, so I guess the can network is decoupled from the obd2 interface. Is there any chance to get access to the can network? Or might I need a different device to do so? Maybe this info helps: I have a 2011 Skoda.
Answer
On many modern vehicles there are actually multiple CAN buses controlling the numerous functions needed by the car. Some of these CAN buses are high-speed for important systems like engine control, and some are low-speed for less critical functions such as climate control (or in your case, diagnostics through the OBD2 port). These multiple CAN buses are usually interconnected through a gateway device in the car that arbitrates which CAN messages can be sent between buses. This is a safety net that prevents lower priority CAN buses from interfering with the more critical CAN buses.
In an example case, the CAN bus used for engine control may be able to communicate with the radio CAN bus so that the radio volume gets increased when the engine is revving to higher RPMs for comfort reasons. This would likely be a one-way connection though the gateway though, as it would be in the interest of safety to not allow the radio's CAN bus to send signals back to the engine (this could lead to potential problems if using aftermarket radios for example).
As a result of everything mentioned above, a connection to the OBD2 port's CAN lines most likely will not have full access to the complete CAN network on your car. One way to confirm this would be to look for the Factory Service Manual for your particular vehicle to see how the CAN bus(es) are setup for your car (there are actually quite a few cars that operate on only a single CAN bus in order to cut costs).
Keep in mind that as an alternative to using the OBD2 port, you can always tap directly into the CAN bus that you are interested in. For example, if you remove the radio from your car to expose the radio harness, you can usually tap directly into the CAN lines for the radio bus with the correct equipment.
Hope this helps!