If you are new to this and wondering why you are not seeing anything on the Diagnostic bus, then this mod won't help because there is nothing to see on that Bus unless you have a diagnostic unit connected. After you remove it CAN H to CAN L should be around 20K. You can check you've got the right one by measuring it and comparing with the resistance between CAN H & CAN L - you should get the same reading. It's a tiny SMD resistor right next to the CAN high screw connection on most boards and may be labelled R3. If you're having trouble reading the low speed buses then try removing the resistor. The value of this resistor seems to vary - I have seen 100R and 1K0, but low values will effectively short out the low speed CAN bus and stop it working. Most of the CAN Shields I've seen are designed to work on the high speed buses and have a resistor across CAN H & CAN L. If you read the Audi training notes you will see there is a subtle difference in voltage levels between the high speed and low speed buses and also the load that these buses expect to see: CAN frame suggests that ignition was on, temperature in my garage was 8 degrees Celsius and vehicle speed was zero, which seems about right.
During the capture, car had ignition on, and engine wasnt running.
Message with ID 0x351 captured on the CAN bus: 8 0 0 0 0 60 60 0. This post discusses using an Arduino with a CAN Shield to interact with the various databuses and how to solve a problem that might exist reading / writing data on the Infotainment & Comfort buses. speed in km/h ( (UV << 8) + LV - 1) / 200.
