×

Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---

Question about worked example - Audi Q7

CANBus Communications Decoded

Forum Posts

Courses

Blog

Tech Articles

Discussion and questions related to the course CAN Bus Communications Decoded

= Resolved threads

Author
426 Views

"So Volkswagen/Audi group vehicles of this era all have a CAN bus point where all the CAN bus wires come together and they're connected by one single connector and that actually joins the network together between all the modules in the car."

Can you expand on this? It seems to describe a hub and spoke type setup, instead of the single path with nodes branching off, which seems to contradict the design as I understand it. Did I misunderstand what the above comment meant, or canbus design requirements?

I'm about to start reversing a same'ish year Audi.

the best way I can explain it is there's rules , and there's laws.

rule : each node should have no longer than a 1 ft branch with a total run length dependent on the can bitrate.

law : each node's transceiver and controller must be able to sync with the bitrate to determine each bit's dominant or recessive state correctly. branch lengths and transceiver capacitance will affect these values.

many manufacturers will break away from standards but still adhere to the laws to have successful operation

Great stuff Mitch.

A less elegant way of putting it is I've seen serious hacked CAN wiring with oddball long lengths and structure function properly, and I've seen carefully constructed harnesses with one little thing out of range, cause a problem. If you follow all the rules, your odds of success increase massively, so that will always be the suggested method, but sometimes you can stray from them and get away with it. OEMs likely perform careful testing to determine if their alterations from ideal methods have been successful.

Okay, so I found the wiring diagram, and if I understand it correctly, this "CAN Disconnect Plug" is just a location on the CAN BUS, where many local nodes tie in to the BUS. Definitely violates the 30cm or 50cm best practices for nodes. There's actually at least two of these disconnect locations.

Thanks guys!

Attached Files

We usually reply within 12hrs (often sooner)

Need Help?

Need help choosing a course?

Experiencing website difficulties?

Or need to contact us for any other reason?