Cannot connect to gateway node of CAN bus through OBD2 port

Question

I wanna connect to can bus of my car. I read in the manuals that obd2 is hooked to high speed can bus of something called CCU node and this CCU node acts as gateway between HS and LS canbus. When i connect to obd2 port canbus via MCP2515 and rotate the ignition key i see no activity, no message comes out of obd2. Am i missing something ? Should not some messages be broadcasting through obd2 port? Or i have to send some requests in advance? My goal is to sniff can messages such as radio, lights, windows and etc.

Answer 1

First, I'd try to check whether the CAN connection has been established in the first place. You could do this by sending the CAN frame 7DF [8] 02 01 00 AA AA AA AA AA – at least one ECU should answer. If that doesn't work, try with the 29-bit broadcast address, try another bitrate, and/or check your wiring.

Once it works, your CAN connection seems to be ok. Still there don't need to be messages on the bus: a) Vehicles contain many CAN busses and the "interesting" ones are typically not connected to the OBD2 port. b) Often there are gateway ECUs employed which shield the critical subsystems from the OBD2 port.