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I've asked a similar question before:

Connecting to car CANbus

Unfortunately I haven't progressed much. The first product I tried was a CANLogger 2000, I got nowhere with it, so I sent it back.

After seeing some youtube videos using USB2CAN, I decided to get one of these, I ordered the cabled to go with it to connect the device to my car via the ODBII socket.

I've been through the set-up on linux with the device recognised and the LED green which indicate's its ready. I've set the bit rate to 500,000 but I see absolutely nothing.

Can any help ? Is this bitrate correct? Is there guide or individuals that could help me?

I've tried using several sites to help me set-up and the kayak software, also cansiffer, but I'm seeing nothing at all.

USB2CAN Setup I've read here:

Volkswagen and Audi technical data The bit rate could be 100kbps, is this actually 125kbps ?

Pᴀᴜʟsᴛᴇʀ2
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SPlatten
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1 Answers1

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I don't see how this is different from your previous question.

No data is actively sent to the OBD port on late VAG vehicles as this in connected to a gateway and only responds to PIDs and manufacture specific data and codes hence why you can't 'sniff' anything on it.

You need to access a CAN bus channel connected directly to a ECU/Module. Find the twisted pair connected to something such as the engine ECU, instrument cluster, BCM etc and see if you can read any data then. The baud rate on the busses connected to the instrument cluster and engine ECU will certainly be 500kbps and any entertainment buses connected to the radio etc could be lower.

Below you can see a very simplified version of a VAG CAN bus network, as you can see there are multiple buses. A convenience bus, a powertrain bus and the OBD wiring. In reality there can be upto 5 buses. It now becomes clear that the diagnostic connector is not connected to a bus as there is only one node (the diagnostic gateway). The OBD port is not connected to any other node, the engine ecu cannot communicate with the radio and as the buses are completely independent from each other all communication between the OBD port or the different buses have to go through the gateway.

The is no data on the OBD port so there is nothing to sniff. When you connect a diagnostic tool it sends a PID request to the gateway which then sends the required data. It's like a call and response system. As you are probably aware PIDs are readily available and can be found anywhere such as wikipedia but these only deal with engine and certain safety systems. So if you want to sniff any raw data you need to connect directly to the bus with the required node on it.

CAN BUS Diagram

Newbie Noob
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  • I know you are not correct. CANbus is just that a bus, messages are sent from a node on the network and the address is in the packet. It is sent to all nodes on the network and each node receives it and evaluates the packet address to see if the address is for it. This is exactly why you can sniff the data. – SPlatten Dec 17 '17 at 19:31
  • Yes true but the OBD port is not a node its a connector it has no intelligence. It is connected to a Diagnostic gateway via a dedicated bus. None of the other nodes are connected directly to the OBD port. What year is your A5? I do not appreciate the down vote as I am correct, NO ECU IS CONNECTED DIRECTLY TO THE OBD PORT on late VAG vehicles and they have multiple CAN buses. – Newbie Noob Dec 17 '17 at 19:42
  • It doesn't need intelligence it is simply a port that can be used to monitor the CANbus network. The A5 is 2012, 2TDi fastback. I've written adapters for several different networks, inc. Modbus, the protocol is different but the way packets are address are very similar. Modbus can run on a multi drop RS485 network, anyone can snifff the data just by hooking up a passive device to receive any data on the port, and this is exactly what I'm trying to do on the ODBII. I spoke to a technician at Audi last week and he told me I should be able to see data when hooked up to the ODBII port. – SPlatten Dec 17 '17 at 19:48
  • Please bear with me I am writing a better answer and making a diagram. I don't think you understand what I am trying to say – Newbie Noob Dec 17 '17 at 19:59
  • Thank you, I'm away from home atm, I will investigate when I return. – SPlatten Dec 17 '17 at 20:42
  • Having tried to connect to my car again today with the module configured correctly and the green LED illuminated, I am still seeing no activity at all. I've tried both "cansniffer" and "candump" but nothing at all. There are various youtube videos showing USB2CAN connected to the ODBII port and logging data, I'm seeing nothing. Can anyone help? – SPlatten Dec 23 '17 at 12:57