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CANBus Communications Decoded

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Discussion and questions related to the course CAN Bus Communications Decoded

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Given that some data are supposed to be transmitted over a CANbus, according to the OBD2 protocols, does anyone know of any reference or documentation describing which messages are (supposed to) be transmitted over the OBD2 CANbus and at which PIDs?

Background is reverse engineering and data logging on stock cars and in this particular case, the ignition advance.


Note to self: Google it first...


Anyone has experience with those PIDs?

Yes -- I use that wikipedia entry a lot to generate / decode OBD2 messages on the CAN bus.

Note there is an ODB query that will return a bitfield of the PIDs supported. So the car can tell you what it can tell you.

Great, Thanks.

It looks like it is a bit involving and needs some getting used to, plus some specific tools, or just a diagnostics tool to do it for you.

You can think of the OBD2 system as a higher level protocol that sits ontop of the CAN comms protocol. The aim of the course is that once completed you'll have the foundations of how the CAN comms protocol sorted, so if you need to work with the higher level protocols (OBD2, CANOpen, J1929, etc), you'll be able to get up to speed much easier.

The course is spot on, clarifying a lot of shady areas of how CAN works on cars. I guess it's not even relevant to go that deep into all the protocols, especially when the basic diagnostics tools do the job for you.

I was just wondering why the data i see, sniffing passively on the OBD2 port, did not seem to be all there should be for a universal diagnostics bus.

David's point, regarding the necessary query to get the data pretty much answers my question. I will try a couple of things with the tools i have lying around, next time i get to it.


CSS Electronics has an OBD2 PID converter i'll reference for use

Online OBD2 PID Converter: Quickly Decode Your Car Data (csselectronics.com)

Great! generally, CSS Elecronics seems to be a good recourse.

Does anybody use the Hardware from CSS? Thought about buying it, but I'm not sure how well it is suites for decoding and reverse engineering a OEM CanBus?

a colleague of mine received a css module (not sure which one). it was broken on arrival and they shipped him another no questions asked after seeing his photo of it broken.

all-in-all, piggybacking the wireshark isn't 'terrible' but also isn't my preference by any means.

peak pcan usb still remains my recommended option, and I generally use socketcan supported hardware for my deeper dives into the CAN Information

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